JP2023548164A - Manufacturing method of super absorbent resin - Google Patents

Abstract

The present invention relates to a method for producing a superabsorbent resin. More specifically, the present invention relates to a method for producing a superabsorbent resin that can reduce the amount of coarse particles with a particle size of more than 850 μm, improve the water content, and exhibit excellent water absorption performance without deviation.

Description

This application is based on Korean Patent Application No. 10-2021-0079644 dated June 18, 2021, Korean Patent Application No. 10-2021-0080233 dated June 21, 2021, and Korean Patent Application No. 10-2021-0080233 dated June 20, 2022. It claims the benefit of priority based on Application No. 10-2022-0074732, and all contents disclosed in the documents of the Korean patent application are included as part of this specification.

The present invention relates to a method for producing a superabsorbent resin. More specifically, the present invention relates to a method for producing a superabsorbent resin that can reduce the content of coarse particles with a particle size of more than 850 μm, improve the water content, and exhibit excellent water absorption performance without deviation.

Super Absorbent Polymer (SAP) is a synthetic polymer substance that has the ability to absorb 500 to 1,000 times its own weight in water. Each product is named by a different name, such as AGM (Absorbent Gel Material). These superabsorbent resins have begun to be put into practical use as sanitary products, and are currently being used as soil water retention agents for gardening, water-stopping materials for civil engineering and construction, sheets for seedling cultivation, freshness-preserving agents in the food distribution field, and for shipping. It is widely used in materials.

Such superabsorbent resins are widely used mainly in the field of sanitary materials such as diapers and sanitary napkins. In the sanitary material, the superabsorbent resin is generally contained in a spread state within the pulp. However, recent efforts have continued to provide sanitary materials such as diapers with thinner thicknesses, and as part of this effort, the pulp content has been reduced, or even gone a step further, no pulp is used at all, so-called pulpless ( Development of products such as pulpress diapers is being actively promoted.

In this way, in the case of sanitary materials where the pulp content is reduced or pulp is not used, superabsorbent resin is contained in a relatively high proportion, and superabsorbent resin particles are contained in multiple layers within the sanitary material. is inevitable. In order for the overall superabsorbent resin particles containing multiple layers to absorb a large amount of liquid such as urine more efficiently, the superabsorbent resin must not only have high water absorption performance but also a fast water absorption rate. It is necessary to show that

On the other hand, such super-absorbent resins generally involve two steps: polymerizing acrylic acid monomers to produce a hydrogel polymer containing a large amount of water, and drying such a hydrogel polymer to obtain the desired amount. The resin particles are produced through a step of pulverizing them into resin particles having a particle size of , and a later surface crosslinking reaction is selectively performed to improve the physical properties.

Generally, the surface crosslinking reaction is carried out by spraying a surface crosslinking solution prepared by adding a crosslinking agent to water onto the surface of the superabsorbent resin, stirring the mixture, and then applying heat to cause the reaction to occur. However, since the surface crosslinking reaction by heating is usually carried out at a high temperature of 140°C or higher, most of the water contained in the super absorbent resin evaporates, resulting in the super absorbent resin being finally produced. The moisture content of the resin decreases significantly. A superabsorbent resin with such a low water content is susceptible to surface damage due to friction between particles that occurs during transportation and storage, which ultimately leads to a decline in the physical properties of the superabsorbent resin. Furthermore, the amount of fine powder generated increases during the product production process using a super absorbent resin with a low water content, resulting in a decrease in process stability and productivity, and a deterioration in product quality.

Therefore, a method has been proposed in which the water content of the superabsorbent resin is increased by performing a hydration step after surface crosslinking. As a method of adding water to improve the water content of a super absorbent resin, a method of directly adding water through a line and a method of adding water using a spray nozzle are mainly used. However, when feeding through a line, the size of the droplets is large, which creates a mixture of large particles with high moisture content and general particles with low moisture content. . In addition, when injecting through a spray nozzle, the water content can be increased evenly, but the small droplet size causes flow, which causes equipment contamination and foreign matter generation. In particular, the smaller the diameter of the nozzle, the smaller the size of droplets generated during spraying, but if the size of the droplets is too small, there is a problem that they may scatter and contaminate the process. Furthermore, when increasing the diameter of the nozzle, and in addition, when the flow rate is low, no atomization takes place and large droplets are formed. However, as the droplet size increases, it becomes difficult to uniformly and sufficiently add water to the superabsorbent resin, resulting in deviations in the physical properties of the superabsorbent resin. In addition, the droplets induce aggregation of surface-crosslinked polymer particles, and a large amount of coarse particles with a particle size of over 850 μm are generated in the final superabsorbent resin. Resulting in clogging and caking.

Furthermore, as another method for increasing the water content of the superabsorbent resin after surface crosslinking, a method of mixing additives such as silica has been proposed. However, since the additives are usually mixed by a dry method, homogeneous mixing is difficult, resulting in deviations in the physical properties and water absorption performance of the superabsorbent resin.

This has led to the development of a manufacturing technology for super absorbent resin that can fundamentally solve these problems, reduce the generation of coarse particles, increase water content, and exhibit excellent water absorption performance without deviation. continues to be requested.

Therefore, the present invention provides a method for producing a superabsorbent resin that can reduce the content of coarse particles with a particle size of more than 850 μm, improve the water content, and exhibit excellent water absorption performance without deviation.

In order to solve the above problems, according to the present invention,
forming a hydrogel polymer in which a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent are crosslinked and polymerized;
A step of producing hydrated superabsorbent resin particles by atomizing the hydrated gel polymer;
drying the hydrated superabsorbent resin particles to produce dry superabsorbent resin particles;
adding a surface crosslinking agent to the dry superabsorbent resin particles and reacting them to form a surface crosslinked layer on at least a portion of the surface of the superabsorbent resin particles;
cooling and adding water to the superabsorbent resin particles on which the surface crosslinked layer has been formed using a spade type cooler;
The spade-shaped cooler includes a transfer space into which the super absorbent resin particles having the surface cross-linked layer are transferred, and includes a rotatable body part and a rotatable body part provided in the body part to accommodate the transfer space. Two nozzles for injecting cooling air and water into the interior, respectively, are provided on the inner wall of the body portion so as to be movable up and down, and the superabsorbent resin particles on which the surface cross-linked layer is formed in the transfer space are moved from bottom to top. a super water absorbent material comprising one or more spade-shaped blades for recessing, and a drive motor connected to the body part to provide driving force, wherein the surface cross-linked layer is formed by the spade-shaped blades in the body part. After pumping up the resin particles, the pumped super absorbent resin particles are caused to fall in the direction of gravity by the rotation of the body section, and are brought into contact with the cooling air and water introduced into the transfer space of the body section. , cooling and adding water to the super absorbent resin particles on which the surface crosslinked layer has been formed;
A method for producing a super absorbent resin is provided.

Further, according to the present invention, there is provided a super absorbent resin produced by the method for producing a super absorbent resin.

According to the method for producing a superabsorbent resin of the present invention, it is possible to provide a superabsorbent resin that exhibits excellent water absorption performance without deviation.

In addition, during the production of super absorbent resin, the amount of coarse particles with a particle size exceeding 850 μm is reduced, making it possible to minimize the amount of dust generated during the manufacturing process. When manufacturing a water-absorbent article, it is possible to improve process efficiency, such as prevention of back filter clogging and caking.

As a result, the superabsorbent resin produced by the above production method can be appropriately used for sanitary materials such as diapers, especially ultra-thin sanitary materials with reduced pulp content.

1 is a schematic diagram schematically showing a side cross-sectional structure of a spade-shaped cooler used in the method for producing a super absorbent resin according to the present invention. It is a schematic diagram which shows roughly the front structure of the said spade type cooler. It is a schematic diagram which shows roughly the rear structure of the said spade type cooler. FIG. 2 is a schematic diagram schematically showing the mixing process that occurs within the body of a spade-type cooler during the cooling and hydration stages in the method for producing a superabsorbent resin according to the present invention.

The terminology used herein is merely used to describe exemplary embodiments and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. As used herein, terms such as "comprising," "comprising," or "having" are intended to specify the presence of implemented features, steps, components, or combinations thereof. It is to be understood that the present invention does not exclude in advance the possibility of the presence or addition of one or more other features, steps, components or combinations thereof.

Furthermore, unless otherwise specified, "normal temperature" in this specification means 25±2°C.

Although the present invention may undergo various modifications and take various forms, it will be described in detail below with reference to specific embodiments. However, it is to be understood that this is not intended to limit the present invention to a particular disclosed form, but includes all modifications, equivalents, and alternatives that fall within the spirit and technical scope of the present invention. .

Hereinafter, the method for producing a superabsorbent resin according to the present invention and the superabsorbent resin produced by the method will be explained in more detail.

Prior to that, the terminology used herein is merely to refer to particular embodiments and is not intended to limit the invention. As used herein, the singular forms also include the plural forms unless the wording clearly indicates to the contrary.

The method for producing a super absorbent resin according to the present invention includes:
a step (step 1) of forming a hydrogel polymer in which a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent are crosslinked and polymerized;
A step of producing hydrated superabsorbent resin particles by atomizing the hydrated gel polymer (step 2);
drying the hydrated superabsorbent resin particles to produce dry superabsorbent resin particles (step 3);
A step of adding a surface crosslinking agent to the dry superabsorbent resin particles and causing a reaction to form a surface crosslinked layer on at least a portion of the surface of the superabsorbent resin particles (step 4);
cooling and adding water to the superabsorbent resin particles on which the surface cross-linked layer has been formed as a result of the step using a spade-type cooler (step 5);
The spade-shaped cooler includes a transfer space into which the super absorbent resin particles having the surface cross-linked layer are transferred, and includes a rotatable body part and a rotatable body part provided in the body part to accommodate the transfer space. Two nozzles for injecting cooling air and water into the interior, respectively, are provided on the inner wall of the body portion so as to be movable up and down, and the superabsorbent resin particles on which the surface cross-linked layer is formed in the transfer space are moved from bottom to top. a super water absorbent material comprising one or more spade-shaped blades for recessing, and a drive motor connected to the body part to provide driving force, wherein the surface cross-linked layer is formed by the spade-shaped blades in the body part. After pumping up the resin particles, the pumped super absorbent resin particles are caused to fall in the direction of gravity by the rotation of the body section, and are brought into contact with the cooling air and water introduced into the transfer space of the body section. Then, the superabsorbent resin particles on which the surface crosslinked layer has been formed are cooled and hydrated.

The term "polymer" or "macromolecule" as used in the specification of the present invention means a polymerized state of a water-soluble ethylenically unsaturated monomer, and includes all water content ranges or A range of particle sizes can be covered.

Further, depending on the context, the term "super absorbent resin" means a crosslinked polymer, or a powder base resin or a hydrogel polymer consisting of super absorbent resin particles obtained by pulverizing the crosslinked polymer. Or, it is used to include all the crosslinked polymers and hydrogel polymers that have been subjected to additional processes such as drying, pulverization, classification, surface crosslinking, etc. to make them suitable for commercialization. Ru.

Furthermore, the term "normal particles" means particles having a particle diameter (or particle size) of 150 μm to 850 μm among super absorbent resin particles, and the term "fine powder" refers to particles having a particle diameter (or particle size) of 150 μm to 850 μm among super absorbent resin particles. means a particle having a particle size. Moreover, the term "coarse particles" means particles having a particle size of more than 850 μm among super absorbent resin particles. The particle size of such superabsorbent resin particles can be measured by the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP220.3 method.

In addition, the term "chopping" refers to cutting a hydrogel polymer into small pieces of millimeter size in order to improve drying efficiency, and is used separately from the process of pulverizing a hydrogel polymer to the level of micrometers or normal particles. Ru.

Note that the term "micronization" refers to pulverizing a hydrogel polymer to a particle size of several tens to several hundred micrometers, and is used separately from "chopping."

As a method for improving the physical properties of superabsorbent resins, a method is mainly used in which the surfaces of superabsorbent resin particles are treated with a surface crosslinking agent and then heated to form a surface crosslinked layer.

However, since the surface crosslinking reaction for forming the surface crosslinked layer is carried out at a high temperature, the water contained in the superabsorbent resin evaporates, resulting in a large decrease in the water content of the superabsorbent resin. When the water content of the superabsorbent resin decreases, surface damage is likely to occur due to friction between particles that occurs during transportation and storage, and as a result, the physical properties of the superabsorbent resin deteriorate. Furthermore, when producing a product using a super absorbent resin with a low water content, the amount of fine powder generated increases during the process, reducing process stability and productivity, leading to a decline in product quality.

In order to solve this problem, methods have been proposed to increase the water content of the superabsorbent resin by cooling and adding water after surface crosslinking, or by mixing an inorganic substance exhibiting hygroscopicity. However, in the case of the conventional water addition method, the droplets generated during the water addition process induce aggregation of surface-crosslinked superabsorbent resin particles, resulting in large particle sizes in the superabsorbent resin that is finally produced. A large amount of coarse particles having . Furthermore, since the method of mixing inorganic substances is usually carried out using a dry mixing method, it is difficult to achieve uniform mixing, resulting in deviations in the physical properties and water absorption performance of the super absorbent resin.

Therefore, the present inventors discovered that a uniform water addition treatment to a superabsorbent resin can prevent deterioration and deviation in the physical properties of the superabsorbent resin and reduce the generation of coarse particles, and developed a spade-type cooler. We focused on the fact that when used, not only is the superabsorbent resin cooled and water added simultaneously, but the entire superabsorbent resin particle is uniformly treated.

In addition, the superabsorbent resin produced by the production method of the present invention has an increased water content, a low content of coarse particles, and excellent water absorption properties such as water retention capacity and water absorption capacity under pressure. It is possible to exhibit rewet characteristics and water absorption speed without deviation.

Hereinafter, each step of the method for producing a superabsorbent resin according to the present invention will be explained in detail.

Stage 1
Step 1 is a step in which a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent are crosslinked and polymerized to form a hydrogel polymer.

Specifically, the water-containing gel polymer includes a step of neutralizing at least some of the acidic groups of a water-soluble ethylenically unsaturated monomer, and a step of neutralizing at least some of the acidic groups of the water-soluble ethylenically unsaturated monomer. Polymerizing a monomer composition prepared by mixing an ethylenically unsaturated monomer with an internal crosslinking agent and a polymerization initiator to form a hydrogel polymer. (Method 1), or by polymerizing a monomer composition containing a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a polymerization initiator, forming a crosslinked polymer of a water-soluble ethylenically unsaturated monomer and an internal crosslinking agent; and neutralizing at least a portion of the acidic groups of the polymer to form a hydrogel polymer. (Method 2).

In method 1, before polymerizing the water-soluble ethylenically unsaturated monomer, at least a portion of the acidic groups in the monomer are neutralized, and then a polymerization reaction is carried out. The polymer has water-containing properties and absorbs surrounding water, so that it can be produced in the form of a hydrogel polymer having a high water content, usually 30% by weight or more.

On the other hand, in method 2, the acidic groups of the water-soluble ethylenically unsaturated monomer are first polymerized to form a polymer in a state where the acidic groups are not neutralized, and then the acidic groups present in the polymer are removed. In a neutralizing manner, the polymers formed after polymerization exhibit low water content and, as a result, are present in a solid state that absorbs little water in the monomer composition. However, it becomes water-containing due to the subsequent neutralization step and becomes a water-containing gel polymer.

In addition, in Method 2, the water-soluble ethylenically unsaturated monomer (e.g., acrylic acid) whose acidic groups are not neutralized is in a liquid state at room temperature, and has a high solubility or miscibility in the solvent (water). Because of its high miscibility, it does not precipitate even at low temperatures. As a result, polymerization is advantageous at low temperatures for a long time, and a polymer having a high molecular weight and a uniform molecular weight distribution can be stably formed.

Furthermore, water-soluble components normally generated during polymer production are easily eluted when the superabsorbent resin comes into contact with a liquid. Therefore, when the content of water-soluble components is high, most of the eluted water-soluble components remain on the surface of the superabsorbent resin, making the superabsorbent resin sticky and reducing liquid permeability. Therefore, it is important to maintain a low content of water-soluble components in terms of liquid permeability, but when polymerization is performed first in an unneutralized state as in method 2, the polymerization of longer chains It is possible to form aggregates, reduce the content of water-soluble components that exist in an uncrosslinked state due to incomplete polymerization and crosslinking, and as a result, the liquid permeability of the superabsorbent resin can be improved.

Alternatively, as in Method 2, polymerization is first performed in a state where the acidic groups of the acrylic monomer are not neutralized to form a polymer, and after neutralization, the polymer is atomized in the presence of a surfactant. Alternatively, when the acidic groups present in the polymer are neutralized after atomization in the presence of a surfactant, or when the acidic groups present in the polymer are neutralized simultaneously with atomization, the surfactant is present in large amounts on the surface of the polymer. By lowering the adhesiveness of the polymer, aggregation between polymer particles can be prevented. As a result, it is possible to grind to a normal particle size level during the atomization process, and since the drying process proceeds after the particle size is crushed to a normal particle size level, the amount of fine powder generated during the process can be significantly reduced. I can do it.

Accordingly, it is preferable to appropriately select the method for producing the hydrogel polymer from Methods 1 and 2 in consideration of the subsequent steps and conditions.

Specifically, method 1 includes the steps of neutralizing at least some of the acidic groups of a water-soluble ethylenically unsaturated monomer; polymerizing a monomer composition including a saturated monomer, an internal crosslinking agent, and a polymerization initiator to form a hydrogel polymer.

The water-soluble ethylenically unsaturated monomer may be any monomer commonly used in the production of superabsorbent resins. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following chemical formula 1:

[Chemical formula 1]
R-COOM'

In the chemical formula 1,
R is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,
M' is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

Preferably, the monomer is one or more selected from the group consisting of (meth)acrylic acid, and monovalent (alkali) metal salts, divalent metal salts, ammonium salts, and organic amine salts of these acids. There may be.

As described above, when (meth)acrylic acid and/or its salt is used as the water-soluble ethylenically unsaturated monomer, it is advantageous that a super absorbent resin with improved water absorption can be obtained. In addition, examples of the monomer include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, or 2-methacryloylethanesulfonic acid. -(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth) Acrylate, polyethylene glycol (meth)acrylate, (N,N)-dimethylaminoethyl (meth)acrylate, (N,N)-dimethylaminopropyl (meth)acrylamide, etc. can be used.

The water-soluble ethylenically unsaturated monomer has an acidic group, and at least a portion of the acidic group is neutralized by a neutralizing agent.

In the production method according to the present invention, in the method 1, the neutralization of at least a part of the acidic groups of the water-soluble ethylenically unsaturated monomer is performed using the water-soluble ethylenically unsaturated monomer having the acidic group. It is carried out during the process of mixing the monomer composition, internal crosslinking agent, polymerization initiator, and neutralizing agent to produce the monomer composition. The monomer composition produced thereby includes a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups, an internal crosslinking agent, and a polymerization initiator.

During the neutralization, it is preferable that the concentration of the water-soluble ethylenically unsaturated monomer having an acidic group is appropriately determined in consideration of the polymerization time and reaction conditions in the subsequent polymerization reaction step. As an example, in the present invention, in a mixture containing the water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, a polymerization initiator, and a neutralizing agent, The concentration may be 20 to 60% by weight, specifically, 20% by weight or more and 60% by weight or less, or 40% by weight or less.

Furthermore, as the neutralizing agent, one or more basic substances capable of neutralizing acidic groups, such as sodium hydroxide, potassium hydroxide, and ammonium hydroxide, can be used.

The degree of neutralization of the water-soluble ethylenically unsaturated monomer refers to the degree to which the acidic groups contained in the water-soluble ethylenically unsaturated monomer are neutralized by the neutralizing agent. If the degree of neutralization is excessively high, neutralized monomers will precipitate, making it difficult for polymerization to proceed smoothly.On the other hand, if the degree of neutralization is excessively low, the water absorption ability of the polymer will be greatly reduced. Instead, it may exhibit elastic rubber-like properties that are difficult to handle. Accordingly, the degree of neutralization of the water-soluble ethylenically unsaturated monomer is preferably selected appropriately depending on the physical properties of the superabsorbent resin to be achieved. As an example, in the present invention, the degree of neutralization of the water-soluble ethylenically unsaturated monomer is 50 to 90 mol%, more specifically, 50 mol% or more, or 60 mol% or more, or 65 mol%. or more, and may be 90 mol% or less, 85 mol% or less, 80 mol% or less, or 75 mol% or less.

On the other hand, the term "internal crosslinking agent" used in this specification is a term used to distinguish from a surface crosslinking agent for crosslinking the surface of super absorbent resin particles, which will be described later. The agent plays the role of introducing crosslinking bonds between the unsaturated bonds of the water-soluble ethylenically unsaturated monomer described above to form a polymer containing a crosslinked structure.

The crosslinking is carried out regardless of whether it is on the surface or inside. However, when the surface crosslinking step of the superabsorbent resin particles described below is performed, the surface of the superabsorbent resin particles finally produced is renewed by the surface crosslinking agent. The superabsorbent resin particles may have a crosslinked structure, and the inside of the superabsorbent resin particles can maintain the structure crosslinked by the internal crosslinking agent.

As the internal crosslinking agent, one or more of polyfunctional acrylate compounds, polyfunctional allyl compounds, and polyfunctional vinyl compounds can be used.

Specifically, the polyfunctional acrylate compounds include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and polyethylene glycol di(meth)acrylate. Acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate , hexanediol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol di(meth)acrylate, dipentaerythritol tri(meth)acrylate , dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin di(meth)acrylate, and glycerin tri(meth)acrylate Examples include acrylate, and any one or a mixture of two or more of these can be used.

Further, specific examples of the polyfunctional allyl compounds include ethylene glycol diallyl ether, diethylene glycol diallyl ether, triethylene glycol diallyl ether, tetraethylene glycol diallyl ether, polyethylene glycol diallyl ether, propylene glycol diallyl ether, and tripropylene glycol. Diallyl ether, polypropylene glycol diallyl ether, butanediol diallyl ether, butylene glycol diallyl ether, hexanediol diallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, pentaerythritol tetraallyl ether, dipentaerythritol diallyl ether, dipentaerythritol triallyl ether Examples include allyl ether, dipentaerythritol tetraallyl ether, dipentaerythritol pentaallyl ether, trimethylolpropane diallyl ether, trimethylolpropane triallyl ether, glycerin diallyl ether, and glycerin triallyl ether, and any one or Mixtures of two or more can be used.

Furthermore, specific examples of polyfunctional vinyl compounds include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, and tripropylene glycol divinyl ether. Vinyl ether, polypropylene glycol divinyl ether, butanediol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, pentaerythritol divinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol divinyl ether, dipentaerythritol trivinyl ether, divinyl ether, Examples include pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, trimethylolpropane divinyl ether, trimethylolpropane trivinyl ether, glycerin divinyl ether, and glycerin trivinyl ether, and any one or a mixture of two or more of these can be used.

In the polyfunctional allyl compound and polyfunctional vinyl compound, two or more unsaturated groups contained in the molecule are unsaturated bonds of a water-soluble ethylenically unsaturated monomer or unsaturated bonds of other internal crosslinking agents. Unlike acrylate compounds that contain an ester bond (-(C=O)O-) in the molecule, it is possible to combine with each other to form a crosslinked structure during the polymerization process, and unlike acrylate compounds that contain an ester bond (-(C=O)O-) in the molecule, it is difficult to neutralize after the polymerization reaction described above. The crosslinking bond can be stably maintained during the process. This increases the gel strength of the produced superabsorbent resin, increases the process stability in the discharge process after polymerization, and makes it possible to minimize the amount of water-soluble components.

Such an internal crosslinking agent can be used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. For example, the internal crosslinking agent may be 0.01 parts by weight or more, or 0.05 parts by weight or more, or 0.1 parts by weight or more and 5 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. parts by weight or less, or 3 parts by weight or less, or 2 parts by weight or less, or 1 part by weight or less, or 0.7 parts by weight or less. If the content of the internal crosslinking agent is too low, crosslinking will not occur sufficiently and it will be difficult to achieve a strength above the appropriate level, and if the content of the internal crosslinking agent is excessively high, the internal crosslinking density will increase to the desired level. It may be difficult to achieve this water retention capacity.

The polymer formed using the internal crosslinking agent has a three-dimensional network structure in which the main chain formed by polymerizing the water-soluble ethylenically unsaturated monomer is crosslinked by the internal crosslinking agent. . In this way, when a polymer has a three-dimensional network structure, the water retention capacity and pressurized water absorption capacity, which are the physical properties of the superabsorbent resin, are improved compared to the case where the polymer has a two-dimensional linear structure that is not additionally crosslinked by an internal crosslinking agent. It can be significantly improved.

Furthermore, during the production of the monomer composition, it is preferable that the polymerization initiator be appropriately selected depending on the polymerization method.

When a thermal polymerization method is used to form a hydrogel polymer, a thermal polymerization initiator is used, and when a photopolymerization method is used, a photoinitiator is used, and a hybrid polymerization method (where all heat and light are removed) is used. When using the above method), both thermal polymerization initiators and photopolymerization initiators can be used. However, depending on the photopolymerization method, a certain amount of heat is generated by light irradiation such as ultraviolet irradiation, and a certain amount of heat is also generated by the progress of the polymerization reaction, which is an exothermic reaction, so a thermal polymerization initiator is additionally used. May be used.

As the photopolymerization initiator, any compound that can form radicals when exposed to light such as ultraviolet rays can be used without any limitations on its composition.

Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl diacetate. Methyl ketal (Benzyl Dimethyl Ketal), One or more selected from the group consisting of acyl phosphine and alpha-aminoketone can be used. Further, specific examples of the acylphosphine include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl(2,4,6-trimethylbenzoyl) ) Phenylphosphinate and the like. A more diverse range of photoinitiators is well defined in UV Coatings: Basics, Recent Developments and New Applications (Elsevier 2007) by Reinhold Schwalm, p. 115, and is not limited to the examples mentioned above. .

Further, as the thermal polymerization initiator, one or more initiators selected from the group consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid can be used. Specifically, examples of persulfate-based initiators include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), and ammonium persulfate (Ammonium persulfate). persulfate; (NH ₄ ) ₂ S ₂ O ₈ ), and examples of azo-based initiators include 2,2-azobis-(2-amidinopropane) dihydrochloride (2,2-azobis(2-amidinopropane) dihydrochloride; 2-amidinopropane) dihydrochloride), 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride ide), 2-(carbamoylazo) Isobutyronitrile (2-(carbamoylazo)isobutylonitrile), 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (2,2-azobis[2-(2-imidazolin-2- yl) propane] dihydrochloride), 4,4-azobis-(4-cyanovaleric acid), and the like. A wider variety of thermal polymerization initiators are well defined in "Principles of Polymerization" by Odian (Wiley, 1981), p. 203, and are not limited to the examples mentioned above.

Such a polymerization initiator can be used in an amount of 2 parts by weight or less based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. That is, if the concentration of the polymerization initiator is too low, the polymerization rate will be slow and a large amount of residual monomer may be extracted into the final product, which is not preferable. On the other hand, if the concentration of the polymerization initiator is higher than the above range, the polymer chains forming the network will become shorter, the content of water-soluble components will increase, and the physical properties of the resin will deteriorate, such as the ability to absorb water under pressure will decrease. This is not desirable because it can be

Furthermore, during the production of the monomer composition, a reducing agent that forms a redox couple with the polymerization initiator is further added.

Specifically, when the polymerization initiator and reducing agent are added to a polymer solution, they react with each other to form radicals. The formed radicals react with the monomers, and the oxidation-reduction reaction between the polymerization initiator and reducing agent is so reactive that even if only trace amounts of polymerization initiator and reducing agent are introduced, Polymerization is initiated, and low-temperature polymerization is possible without the need to increase the process temperature, and changes in physical properties of the polymer solution can be minimized.

The polymerization reaction using the oxidation-reduction reaction can occur smoothly even at temperatures around room temperature (25° C.) or lower. As an example, the polymerization reaction is performed at a temperature of 5°C or more and 25°C or less, or 5°C or more and 20°C or less.

When a persulfate polymerization initiator is used as the polymerization initiator, examples of the reducing agent include sodium metabisulfite (Na ₂ S ₂ O ₅ ); tetramethylethylenediamine (TMEDA); iron (II) sulfate (FeSO ₄ ); mixture of iron(II) sulfate and EDTA (FeSO ₄ /EDTA); sodium formaldehyde sulfoxylate; and disodium 2-hydroxy-2-sulfinoacetate (Disodium 2-hydroxy-2); -sulfinoacteate) may be used.

Also, potassium persulfate is used as the polymerization initiator, and disodium 2-hydroxy-2-sulfinoacetate is used as the reducing agent; ammonium persulfate is used as the polymerization initiator, and tetramethyl Ethylenediamine may be used; sodium persulfate may be used as a polymerization initiator and sodium formaldehyde sulfoxylate may be used as a reducing agent.

Furthermore, when a hydrogen peroxide-based initiator is used as the polymerization initiator, examples of reducing agents include ascorbic acid; sucrose; sodium sulfite (Na ₂ SO ₃ ), and sodium metabisulfite ( Tetramethylethylenediamine (TMEDA); _Mixture of iron (II) sulfate and EDTA ( _{FeSO 4} /EDTA); Sodium formaldehyde sulfoxylate; Disodium 2 _- hydroxy-2 - Sulfinoacetate (Disodium 2-hydroxy-2-sulfinoacteate); and Disodium 2-hydroxy-2-sulfoacetate (Disodium 2-hydroxy-2-sulfoacetate) Good too.

Additionally, during the preparation of the monomer composition, additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant may be added as necessary.

In the present invention, the monomer composition may be in the form of a solution dissolved in a solvent such as water, and the solid content in the monomer composition in such a solution state, that is, the monomer The concentrations of the polymer, internal crosslinking agent, and polymerization initiator can be appropriately adjusted by taking into account the polymerization time, reaction conditions, and the like. For example, the solids content in the monomer composition may be 10 to 80% by weight, or 15 to 60% by weight, or 30 to 50% by weight. When the monomer composition has a solid content in this range, the gel effect phenomenon that appears in the polymerization reaction of a highly concentrated aqueous solution can be used to eliminate the need to remove unreacted monomers after polymerization. However, it may be advantageous for adjusting the pulverization efficiency during pulverization of the polymer, which will be described later.

At this time, the solvent that can be used is not limited in structure as long as it can dissolve the above-mentioned raw material. For example, the solvent includes water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, Methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, or a mixture thereof can be used.

Next, the polymerization step for the monomer composition can be carried out without particular configuration limitations as long as a hydrogel polymer can be formed by thermal polymerization, photopolymerization, or hybrid polymerization.

Specifically, polymerization methods are broadly divided into thermal polymerization and photopolymerization depending on the polymerization energy source. Usually, when thermal polymerization is advanced, it is carried out in a reactor with a stirring shaft such as a kneader, and photopolymerization If the process is carried out, it may be carried out in a reactor equipped with a movable conveyor belt or in a flat-bottomed vessel.

In such a polymerization method, a polymer having a relatively short polymerization reaction time (eg, 1 hour or less) does not have a large molecular weight and has a wide molecular weight distribution.

As an example, as mentioned above, a hydrogel polymer obtained by thermal polymerization by supplying hot air to a reactor such as a kneader equipped with a stirring shaft or by heating the reactor can be reacted. Depending on the configuration of the stirring shaft provided in the vessel, the hydrogel polymer discharged to the outlet of the reactor may be in the form of several centimeters to several millimeters. Specifically, the size of the obtained hydrogel polymer varies depending on the concentration and injection speed of the monomer composition injected, but it is usually a hydrogel polymer with a weight average particle size of 2 to 50 mm. A gel polymer is obtained.

In addition, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt or a flat-bottomed container as described above, the form of the hydrogel polymer that is usually obtained is a sheet-like hydrous gel polymer with the width of the belt. It may also be a gel polymer. At this time, the thickness of the polymer sheet varies depending on the concentration of the monomer composition injected and the injection speed or amount, but it is usually a sheet-like polymer sheet having a thickness of about 0.5 to about 5 cm. Preferably, the monomer composition is fed in such a way that coalescence is obtained. If the monomer composition is supplied to the extent that the thickness of the sheet-shaped polymer is too thin, the production efficiency will be low, which is undesirable, and if the thickness of the sheet-shaped polymer exceeds 5 cm, Due to the large thickness, the polymerization reaction may not occur evenly throughout the thickness.

Furthermore, in polymerization in a reactor with a reactor stirring shaft equipped with a conventional conveyor belt, a new monomer composition is supplied to the reactor while the polymerization product is moved, and the polymerization is carried out in a continuous manner. , polymers having different polymerization rates are mixed, which makes it difficult to uniformly polymerize the entire monomer composition, resulting in overall deterioration of physical properties.

Accordingly, in the manufacturing method of the present invention, the polymerization reaction of the monomer composition is performed in a batch type reactor.

As described above, by performing the polymerization in a fixed-bed type in a batch reactor, there is less possibility that polymers having different polymerization rates will be mixed together, and thereby a polymer having uniform quality can be obtained.

Further, when the polymerization reaction is carried out in a batch reactor, the polymerization reaction is carried out for a longer time, for example, 3 hours or more, than in the case where the polymerization is carried out continuously in a reactor equipped with a conveyor belt. However, despite such a long polymerization reaction time, the polymerization is performed on unneutralized water-soluble ethylenically unsaturated monomers, so even if polymerization is performed for a long time, the monomers remain It does not precipitate and is therefore advantageous in carrying out polymerization over a long period of time.

Meanwhile, a thermal polymerization method may be used for the polymerization in the batch reactor, whereby a thermal polymerization initiator is used as the polymerization initiator. The thermal polymerization initiator is as described above.

On the other hand, method 2 for producing a hydrogel polymer involves polymerizing a monomer composition containing a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a polymerization initiator. forming a polymer in which the water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent are crosslinked; and neutralizing at least a portion of the acidic groups of the polymer to form a hydrogel polymer. This is done in a step of forming a .

In Method 2, the monomer composition is prepared in the same manner as in Method 1, except that a water-soluble ethylenically unsaturated monomer whose acidic groups are not neutralized is used during the production of the monomer composition. The production of products and the polymerization process for them are carried out.

Further, the polymerization reaction in Method 2 is specifically performed in a batch reactor. Furthermore, in the polymerization in the batch reactor, a thermal polymerization method can be used, so that a thermal polymerization initiator can be used as the polymerization initiator. Note that, as described above, polymerization can be initiated by adding a reducing agent together with the initiator.

Next, in method 2, the step of neutralizing at least part of the acidic groups of the cross-linked polymer to produce a hydrogel polymer includes applying a neutralizing agent to the cross-linked polymer. This is done by introducing and reacting.

As the neutralizing agent, as in Method 1, basic substances capable of neutralizing acidic groups, such as sodium hydroxide, potassium hydroxide, and ammonium hydroxide, can be used.

In addition, if the degree of neutralization of the polymer, which refers to the extent to which the acidic groups contained in the polymer are neutralized by the neutralizing agent, is too high, the concentration of carboxyl groups on the particle surface is excessively low. Therefore, surface crosslinking in subsequent steps is difficult to be carried out successfully, and as a result, water absorption properties and liquid permeability under pressure may be reduced. On the other hand, if the degree of neutralization of the polymer is too low, not only will the water absorption capacity of the polymer be greatly reduced, but it may also exhibit elastic rubber-like properties that are difficult to handle. Accordingly, it is preferable that the degree of neutralization of the polymer is appropriately selected depending on the physical properties of the superabsorbent resin to be achieved. As an example, in the present invention, the degree of neutralization of the polymer is 50 to 90 mol%, more specifically, 50 mol% or more, or 60 mol% or more, or 65 mol% or more, and 90 mol%. or less, or less than or equal to 85 mol%, or less than or equal to 80 mol%, or less than or equal to 75 mol%.

The polymers produced by Method 1 and Method 2 have a water content of 30 to 80% by weight in a hydrogel state, more specifically, 30% by weight or more, or 35% by weight or more, or 40% by weight or more. and is 80% by weight or less, or 75% by weight or less, or 70% by weight or less.

If the water content of the hydrogel polymer is too low, it may be difficult to secure an appropriate surface area in the subsequent pulverization step, so that it may not be effectively pulverized, and if the water content of the hydrogel polymer is too high. , the pressure experienced in the subsequent grinding step increases, making it difficult to grind to the desired particle size. However, the hydrogel polymer produced by the production method according to the present invention has a water content that satisfies the above range conditions and is suitable for the subsequent atomization step.

On the other hand, throughout this specification, "water content" refers to the water content relative to the total weight of the hydrogel polymer, and is the value obtained by subtracting the weight of the dry polymer from the weight of the hydrogel polymer. means. Specifically, it is defined as a value calculated by measuring the weight loss due to water evaporation in the polymer during the process of raising the temperature of the polymer in crumb state using infrared heating and drying it. At this time, the drying conditions were to raise the temperature from room temperature to about 180°C and then maintain it at 180°C.The total drying time was set to 40 minutes, including 5 minutes during the temperature rise stage, and the moisture content Measure. The specific measurement method and conditions are as explained in the experimental examples below.

Stage 2
Next, in step 2, the hydrogel polymer produced in step 1 is atomized to produce hydrous superabsorbent resin particles.

In this step, the hydrogel polymer is not chopped into millimeter-sized pieces, but is simultaneously chopped into pieces with a size of several tens to hundreds of micrometers and agglomerated. In other words, it is a stage in which secondary agglomerated particles are produced by agglomerating multiple primary particles finely chopped into sizes of tens to hundreds of micrometers by imparting appropriate adhesiveness to the hydrogel polymer. . The water-containing superabsorbent resin particles, which are secondary agglomerated particles produced in such a step, have a normal particle size distribution, have a large increase in surface area, and can significantly improve the water absorption rate.

Specifically, in the production method of the present invention, the step of atomizing the polymer to produce hydrated superabsorbent resin particles is performed two or more times, more specifically, two to four times.

The atomization step is performed by an atomization device, and the atomization device includes a body portion including a transfer space into which the polymer is transferred, and a body portion rotatably installed inside the transfer space to transfer the polymer. a screw member that moves the screw member, a drive motor that provides rotational driving force to the screw member, a cutter member that is provided in the body portion and that crushes the polymer, and a cutter member that crushes the polymer that has been crushed by the cutter member. The perforated plate may be discharged to the outside of the body part and may include a perforated plate having a plurality of holes formed therein. At this time, the size of the holes provided in the perforated plate of the atomization device may be 1 mm to 10 mm, or 1 to 6 mm.

Further, the atomization step is performed in the presence of a surfactant.

The surfactant adsorbs or binds to the surface of the hydrogel polymer to reduce the tackiness of the surface of the hydrogel polymer, and as a result, controls the aggregation of the crushed hydrogel polymers.

Conventionally, particles of several mm or several cm have been formed in a chopping process for hydrogel polymers. Although the surface area of the hydrogel polymer can be increased to some extent by such a chopping process, it is difficult to expect an effect that can effectively improve the water absorption rate. Therefore, in order to improve the water absorption rate, a method was proposed in which the surface area was increased by increasing the mechanical force and kneading in the chopping stage, but in this case, the stickiness characteristic of the polymer caused excessive agglomeration. After chopping, drying, and pulverization, amorphous single particles with uneven surfaces were formed, and excessive kneading or crushing resulted in an increase in water-soluble components.

Therefore, in the present invention, a large amount of the surfactant is present on the surface of the hydrogel polymer by performing the atomization step on the hydrogel polymer in the presence of a surfactant. The surfactant present on the surface of the hydrogel polymer can prevent the polymer from excessively aggregating by reducing the high tackiness of the polymer, and can adjust the aggregation state to a desired level. . As a result, unlike the conventional chopping process consisting of micrometer units, the hydrogel polymer can be crushed from several millimeters to hundreds of micrometers in size, and the subsequent crushing can be carried out under milder conditions. and a drying process, and the amount of fine powder generated during the manufacturing process can be significantly reduced.

On the other hand, when a hydrogel polymer is atomized in the presence of a surfactant, due to the high water content of the hydrogel polymer, the surfactant is present inside the hydrogel polymer rather than at the interface of the hydrogel polymer. The surfactant may not be able to fully fulfill its role. In contrast, in the present invention, such problems have been solved by using an atomization device having the above-mentioned characteristic structure.

In addition, the hydrophobic functional group contained in the surfactant imparts hydrophobicity to the surface of the pulverized superabsorbent resin particles and alleviates the frictional force between the particles. The apparent density of the resin can be increased, and the hydrophilic functional group portion contained in the surfactant also binds to the superabsorbent resin particles and prevents a decrease in the surface tension of the superabsorbent resin. I can do it. As a result, the superabsorbent resin produced by the production method of the present invention can exhibit a higher apparent density while exhibiting the same level of surface tension compared to a superabsorbent resin that does not use a surfactant. .

Specifically, as the surfactant, a compound represented by the following chemical formula 2 or a salt thereof can be used, but the present invention is not limited thereto:

In the chemical formula 2,
A ₁ , A ₂ and A ₃ are each independently a single bond, carbonyl,

and one or more of these is carbonyl or

, where m1, m2 and m3 are each independently an integer from 1 to 8,

are connected to each adjacent oxygen atom,

is connected to adjacent R ₁ , R ₂ and R ₃ , respectively,

R ₁ , R ₂ and R ₃ are each independently hydrogen, a straight-chain or branched alkyl having 6 to 18 carbon atoms, or a straight-chain or branched alkenyl having 6 to 18 carbon atoms;
n is an integer from 1 to 9.

The surfactant is mixed with the polymer and added so that the atomization step can be easily performed without agglomeration.

The surfactant represented by the chemical formula 2 is a nonionic surfactant, and has excellent surface adsorption performance due to hydrogen bonding force even with unneutralized polymers, thereby achieving the desired aggregation control effect. suitable for On the other hand, in the case of anionic surfactants that are not nonionic surfactants, when mixed with a polymer neutralized with a neutralizing agent such as NaOH or _Na2SO4 , carboxyl group substitution of the polymer may occur _. When adsorbed via Na+ ions ionized to the group and mixed into an unneutralized polymer, the adsorption efficiency to the polymer decreases relatively due to competition with the anion of the carboxyl group substituent of the polymer. There's a problem.

Specifically, in the surfactant represented by the chemical formula 2, the hydrophobic functional groups are terminal functional groups R ₁ , R ₂ , and R ₃ (if not hydrogen), and the hydrophilic functional groups are , further contains a glycerol-derived moiety in the chain and a terminal hydroxyl group (n = 1 to 3 when A _n is a single bond and R _n is hydrogen at the same time); The hydroxyl group is a hydrophilic functional group that plays a role in improving the adsorption performance on the surface of the polymer. Thereby, agglomeration of super absorbent resin particles can be effectively suppressed.

In the chemical formula 2, the hydrophobic functional groups R ₁ , R ₂ , and R ₃ (if not hydrogen) are each independently a straight or branched alkyl group having 6 to 18 carbon atoms, or 6 to 18 straight or branched chain alkenyl. At this time, if R ₁ , R ₂ , and R ₃ moieties (if not hydrogen) are alkyl or alkenyl having less than 6 carbon atoms, the chain length is short and aggregation of the pulverized particles cannot be effectively controlled. Problematically, when R ₁ , R ₂ , R ₃ moieties (if not hydrogen) are alkyl or alkenyl having more than 18 carbon atoms, the mobility of the surfactant is reduced and it does not interact effectively with the polymer. There is a problem that the unit price of the composition increases due to the increase in the cost of the surfactant.

Preferably, when R ₁ , R ₂ and R ₃ are hydrogen or straight-chain or branched alkyl having 6 to 18 carbon atoms, 2-methylhexyl, n-heptyl, 2-methylheptyl , n-octyl, n-nonyl, n-decanyl, n-undecanyl, n-dodecanyl, n-tridecanyl, n-tetradecanyl, n-pentadecanyl, n-hexadecanyl, n-heptadecanyl, or n-octadecanyl. or straight chain or branched alkenyl having 6 to 18 carbon atoms, 2-hexenyl, 2-heptenyl, 2-octenyl, 2-nonenyl, n-dekenyl, 2-undekenyl, 2-dodekenyl, 2 -tridekenyl, 2-tetradekenyl, 2-pentadekenyl, 2-hexadekenyl, 2-heptadekenyl, or 2-octadekenyl.

The surfactant is selected from compounds represented by the following chemical formulas 2-1 to 2-14:

On the other hand, the surfactant can be used in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the hydrogel polymer. If too little of the surfactant is used, it will not be evenly adsorbed onto the surface of the polymer, and particles will re-agglomerate after pulverization; if too much of the surfactant is used, the final The physical properties of the superabsorbent resin produced may deteriorate. For example, the surfactant is 0.01 parts by weight or more, or 0.015 parts by weight or more, or 0.1 parts by weight or more and 5 parts by weight or less, or 3 parts by weight, based on 100 parts by weight of the polymer. parts by weight or less, or 2 parts by weight or less, or 1 part by weight or less, or 0.5 parts by weight or less.

The method of mixing such a surfactant with a polymer is not particularly limited as long as it can be mixed evenly with the polymer, and any method can be appropriately adopted and used. Specifically, the surfactant may be mixed dry, dissolved in a solvent and then mixed in a solution state, or melted and then mixed.

Among these, for example, the surfactant can be mixed in the form of a solution dissolved in a solvent. At this time, as the solvent, all kinds of inorganic or organic solvents can be used without limitation, but water is the most suitable in consideration of the ease of the drying process and the cost of the solvent recovery system. The solution can be prepared by mixing the surfactant and the polymer in a reaction tank, or by putting the polymer in a mixer and spraying the solution, or by mixing the polymer and the solution in a continuously operated mixer. A method of continuously supplying and mixing can be used.

On the other hand, in the production method of the present invention, in method 2 of step 1, the step of neutralizing at least a part of the acidic groups of the polymer and the step of atomizing the polymer in the presence of the surfactant are , may be performed sequentially, alternately, or simultaneously.

In other words, a neutralizing agent is added to the polymer to neutralize the acidic groups first, and then a surfactant is added to the neutralized polymer to make the polymer mixed with the surfactant into fine particles. Alternatively, a neutralizing agent and a surfactant may be added to the polymer at the same time to neutralize and atomize the polymer. Alternatively, the surfactant may be added first and the neutralizing agent may be added later. Alternatively, the neutralizing agent and the surfactant may be added alternately. Alternatively, a surfactant may be added first to atomize the particles, then a neutralizing agent may be added for neutralization, and a surfactant may be additionally added to the neutralized hydrogel polymer in the atomization step. may be performed additionally.

However, in order to uniformly neutralize the entire polymer, it is preferable to leave a certain time difference between the addition of the neutralizing agent and the atomization step.

On the other hand, by adding the surfactant, at least a portion or a considerable amount of the surfactant can be present on the surface of the hydrated superabsorbent resin particles.

Here, the presence of the surfactant on the surface of the hydrated superabsorbent resin particles means that at least a portion or a considerable amount of the surfactant is adsorbed or bonded to the surface of the hydrated superabsorbent resin particles. It means there is. Specifically, the surfactant may be physically or chemically adsorbed on the surface of the hydrated superabsorbent resin particles. More specifically, the hydrophilic functional group of the surfactant is attached to the hydrophilic portion of the surface of the hydrated superabsorbent resin particle by intermolecular force such as dipole-dipole interaction. It may be physically adsorbed. In this way, the hydrophilic portion of the surfactant is physically adsorbed to and surrounds the surface of the hydrated superabsorbent resin particles, and the hydrophobic portion of the surfactant is not adsorbed to the surface of the resin particles. The hydrated superabsorbent resin particles may have a type of micelle structure and may be coated with a surfactant. This is because the surfactant is not added during the polymerization process of the water-soluble ethylenically unsaturated monomer, but is added at the atomization stage after polymer formation. Compared to the case where the surfactant is present inside the polymer when it is added during the process, it can fulfill its role as a surfactant more faithfully, and pulverization and agglomeration occur simultaneously, resulting in fine particles being agglomerated. Particles with a large surface area can be obtained.

After mixing the polymer and the surfactant in this way, or by atomizing the polymer in the presence of the surfactant, the superabsorbent resin particles and the surfactant are mixed together. It is possible to produce water-containing superabsorbent resin particles in the form of secondary agglomerated particles that are finely chopped and aggregated.

Here, "water-containing super absorbent resin particles" are particles having a water content (water content) of approximately 30% by weight or more, and are particles obtained by cutting and aggregating a water-containing gel polymer into particles without a drying process. Therefore, like the hydrogel polymer, it can have a water content of 30 to 80% by weight. More specifically, it is 30% by weight or more, or 35% by weight or more, or 40% by weight or more, and 80% by weight or less, or 75% by weight or less, or 70% by weight or less.

In the manufacturing method according to the present invention, in addition to the surfactant, one or more additives selected from metal hydroxides and metal salts may be selectively added during the atomization step.

The metal hydroxide functions to provide water absorption ability by forming osmotic pressure during the atomization process. Specific examples include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and any one or a mixture of two or more of these can be used.

Further, the metal salt functions to remove residual monomer during the atomization process. Specific examples include alkali metal sulfates such as sodium sulfite, sodium persulfate, and potassium persulfate; or ammonium sulfate-based compounds such as ammonium persulfate. , any one or a mixture of two or more of these can be used.

The additive may be used in an amount of 0.01 to 20 parts by weight based on 100 parts by weight of the hydrogel polymer. If too little of the additive is used, the effect of using the additive will be slight, and if too much of the additive is used, the physical properties of the final superabsorbent resin will be affected. may decrease. More specifically, the additive is 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.1 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the hydrogel polymer. , or 15 parts by weight or less, or 13 parts by weight or less, or 10 parts by weight or less, or 6 parts by weight or less.

Similar to the method of adding the surfactant, the additive is mixed with the polymer in a dry manner, dissolved in a solvent and then mixed in a solution state, or dispersed in a dispersion medium and mixed. Or it can be melted and then mixed with the polymer.

Further, when the atomization step is performed two or more times, the additives may be added to each atomization step in the same or different amounts. For example, when the atomization step is performed four times, the atomization step includes a first atomization step in which the hydrogel polymer is first atomized using the atomization device without adding surfactant and additives. a second atomization step of secondary atomization of the first atomized hydrogel polymer using the atomization device under conditions of introducing metal hydroxide; a third atomization step of tertiary atomization of the second atomized hydrogel polymer using an atomization device; This is carried out in a fourth atomization step in which the hydrogel polymer is subjected to quaternary atomization. The amounts of the surfactant and additives added in each step are as described above, and the order of the first to fourth atomization steps can be changed.

When the atomization step is carried out in this manner, it is possible to achieve the same level of particle size distribution as the product after drying, thereby further reducing the generation of fine powder.

Accordingly, the manufacturing method according to the present invention may not include an additional grinding step after the atomization step. Further, since the fine powder content in the water-containing superabsorbent resin particles obtained after the atomization step is low, an additional classification step may not be included. In other words, it is possible to produce a superabsorbent resin having a particle size suitable for products without additional grinding and classification steps. However, depending on the application to which the product is applied and if necessary, pulverization may be additionally carried out or a classification step may be additionally carried out.

Stage 3
Next, step 3 is a step of drying the hydrated superabsorbent resin particles to produce dry superabsorbent resin particles.

In a conventional method for producing a superabsorbent resin, the drying step is generally performed until the water content of the superabsorbent resin becomes less than 10% by weight. However, in the production method according to the present invention, the drying step is performed so that the water content of the superabsorbent resin after drying is 10% by weight or more based on the total weight of the dried superabsorbent resin particles, more specifically, 10% by weight or more based on the total weight of the dried superabsorbent resin particles. ~20% by weight, or 10~15% by weight.

To this end, the drying is performed at 80 to 250° C. for 5 to 80 minutes. If the drying temperature is too low, the drying time becomes long and the process efficiency is reduced. If the drying temperature is too high, the water content of the superabsorbent resin particles becomes too low and the subsequent Breakage may occur during the process. More specifically, the drying is performed at a temperature of 80°C or higher, or 100°C or higher, or 120°C or higher and 250°C or lower, or 180°C or lower, or 150°C or lower for 5 minutes or more, or 20 minutes or more. And, the duration is 80 minutes or less, or 60 minutes or less.

Further, the drying is performed using a moving type. Such moving type drying is classified as fixed-bed type drying based on whether or not the material moves during drying.

The moving type drying refers to a method of drying the dried material while mechanically stirring it. At this time, the direction in which the hot air passes through the substance may be the same as or different from the circulation direction of the substance. Alternatively, the material may be circulated inside the dryer and a heat transfer fluid (heat carrier flow) may be passed through a separate pipe tube outside the dryer to dry the material. On the other hand, in fixed-bed drying, the material to be dried is stopped at the bottom of a perforated iron plate through which air can pass, and hot air is passed through the material from the bottom to the top. Refers to the method of drying.

Therefore, it is preferable to use a fluidized drying method in order to prevent agglomeration between the water-containing superabsorbent resin particles to be dried in the drying step and to complete drying within a short period of time.

Devices that can be dried using this fluidized drying method include horizontal-type mixer dryers, rotary kilns, paddle dryers, steam tube dryers, etc. A fluidized fluid dryer can be used.

By controlling the rotation speed by using the fluidized drying method, drying efficiency can be further improved. As an example, the rotation speed may be 10 rpm or more, or 30 rpm or more, or 50 rpm or more, or 80 rpm or more and 200 rpm or less, or 150 rpm or less, or 120 rpm or less, or 100 rpm or less, and the It is preferable that the drying conditions are determined in consideration of the water content of the gel polymer, the amount of the hydrous gel polymer, the type of fluidized drying device, the drying temperature, the drying time, etc.

As described above, the drying process yields dried superabsorbent resin particles having a higher water content than conventional ones. Specifically, the moisture content of the dry superabsorbent resin particles is 10% by weight or more, more specifically, 10 to 20% by weight, or 10 to 15% by weight, and the moisture content is within the above range. By having a high rate, the generation of fines can be prevented or minimized during subsequent steps.

Stage 4
Next, step 4 is a step in which a surface crosslinking agent is added to the dry superabsorbent resin particles to cause a surface crosslinking reaction.

In the step, the crosslinked polymer contained in the dry superabsorbent resin particles is additionally crosslinked with a surface crosslinking agent interposed, so that a surface crosslinked layer is formed on at least a part of the surface of the dry superabsorbent resin particles. It is formed.

As the surface crosslinking agent, all surface crosslinking agents that have been used in the production of superabsorbent resins can be used without any particular limitations. For example, the surface crosslinking agent may include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2 - selected from the group consisting of methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol and glycerol. one or more polyols; one or more carbonate compounds selected from the group consisting of ethylene carbonate, propylene carbonate and glycerol carbonate; epoxy compounds such as ethylene glycol diglycidyl ether; oxazoline compounds such as oxazolidinone; polyamine compounds; oxazoline compounds; mono-, di- or polyoxazolidinone compounds; or cyclic urea compounds; and the like.

Specifically, as the surface crosslinking agent, one or more types, two or more types, or three or more types of the above-mentioned surface crosslinking agents can be used. As an example, ethylene glycol diglycidyl ether and propylene glycol can be used in combination.

Such a surface crosslinking agent can be used in an amount of 0.001 to 5 parts by weight based on 100 parts by weight of the dry superabsorbent resin particles. More specifically, the surface crosslinking agent is 0.001 parts by weight or more, or 0.01 parts by weight or more, or 0.1 parts by weight or more, or 0 parts by weight, based on 100 parts by weight of the dry superabsorbent resin particles. It can be used in a content of .3 parts by weight or more, or 0.4 parts by weight or more and/or 5 parts by weight or less, or 3 parts by weight or less, or 1 part by weight or less. By adjusting the content range of the surface crosslinking agent within the above-mentioned range, a super absorbent resin exhibiting excellent water absorption properties can be produced.

Also, forming the surface crosslinking layer may be performed by adding an inorganic material to the surface crosslinking agent. That is, in the presence of the surface crosslinking agent and the inorganic substance, the surface of the superabsorbent resin particles may be additionally crosslinked to form a surface crosslinked layer.

As such an inorganic substance, one or more inorganic substances selected from the group consisting of silica, clay, alumina, silica-alumina composite, titania, zinc oxide, and aluminum sulfate are used. be able to. The inorganic substances can be used in powder or liquid form, in particular as alumina powder, silica-alumina powder, titania powder or nano-silica solution.

The inorganic substance is 0.001 to 1 part by weight, more specifically, 0.001 part by weight or more, or 0.01 part by weight or more, or 0.001 to 1 part by weight, based on 100 parts by weight of the dry superabsorbent resin particles. It can be used in a content of 1 part by weight or more and 1 part by weight or less, or 0.5 part by weight or less.

Regarding the method of mixing the surface crosslinking agent into the superabsorbent resin particles, there are no limitations on the structure. For example, the surface cross-linking agent and super-absorbent resin particles are mixed in a reaction tank, the surface-cross-linking agent is injected onto the super-absorbent resin particles, or the super-absorbent resin particles are mixed in a continuously operated mixer. A method of continuously supplying and mixing the surface crosslinking agent and the like can be used.

When mixing the surface crosslinking agent and super absorbent resin particles, water and methanol may be added together. When water and methanol are added, there is an advantage that the surface crosslinking agent can be uniformly dispersed in the superabsorbent resin particles. At this time, the added water and methanol content induces uniform dispersion of the surface cross-linking agent, prevents the superabsorbent resin particle clumping phenomenon, and at the same time optimizes the surface penetration depth of the cross-linking agent. can be adjusted appropriately.

The surface crosslinking process is performed at a temperature of 80°C to 250°C. More specifically, the surface crosslinking step is performed at a temperature of 100° C. to 220° C., or 120° C. to 200° C., for 20 minutes to 2 hours, or 40 minutes to 80 minutes. When the above-mentioned surface cross-linking process conditions are satisfied, the surface of the super-absorbent resin particles is sufficiently cross-linked, and the pressurized water absorption capacity can be increased.

The heating means for the surface crosslinking reaction is not particularly limited. Heating can be achieved by supplying a heating medium or by directly supplying a heat source. At this time, the types of heat medium that can be used include, but are not limited to, heated fluids such as steam, hot air, and hot oil. The temperature can be appropriately selected in consideration of the heating medium, heating rate, and target heating temperature. On the other hand, heat sources that are directly supplied include heating methods using electricity and heating methods using gas, but are not limited to the above-mentioned examples.

Stage 5
Next, step 5 is a step in which the superabsorbent resin particles on which the surface crosslinked layer has been formed as a result of step 4 are simultaneously cooled and hydrated using a spade type cooler.

Conventionally, a paddle-type cooler has been mainly used to cool the superabsorbent resin after the surface crosslinking reaction. A paddle-type cooler is equipped with one or more rotating shafts in the longitudinal direction of the cooler inside the cooler, and the rotating shaft is provided with a plurality of paddles or paddle-shaped blades, so that the rotating shaft is As the paddle rotates, the superabsorbent resin particles inside the cooler are stirred and mixed with the cooling water, thereby being cooled. However, in paddle type coolers, stirring and mixing are performed by paddles that rotate along the rotation axis inside the cooler, so superabsorbent resin particles and cooling water can only be stirred and mixed within the rotation radius of the paddles. happen. As a result, contact between the superabsorbent resin particles and cooling water and addition of water to the superabsorbent resin particles are difficult to be carried out sufficiently uniformly over the entire superabsorbent resin particles. In addition, aggregation between superabsorbent resin particles tends to occur during stirring and mixing, and the resulting superabsorbent resin contains a high content of coarse particles with a particle size of more than 850 μm. The physical properties decreased and the deviation was large.

In contrast, in the present invention, a spade-type cooler is used that can uniformly cool and add water to the entire superabsorbent resin particles on which a surface cross-linked layer has been formed, and can evenly mix the additional additives. Use.

The spade-shaped cooler includes a rotatable body part and one or more spade-shaped blades provided on an inner wall of the body part so as to be movable up and down. As a result, when super absorbent resin particles with a surface cross-linked layer are introduced into the body for cooling and adding water, the body rotates, and the spade-shaped blade also rotates. Drives up and down while rotating. By vertically driving the spade-shaped blade, the superabsorbent resin particles in the body are drawn up from bottom to top, and later fall in the direction of gravity due to the rotation of the body. At this time, the superabsorbent resin particles falling in the direction of gravity are cooled and hydrated while coming into contact with the cooling air and water introduced into the body, so that uniform cooling and hydration can be applied to the entire particles. Furthermore, when additives for improving the physical properties of the superabsorbent resin particles are further added selectively, uniform mixing with the additives is also possible.

In addition, unlike conventional paddle-type coolers, the spade-type cooler allows the super-absorbent resin particles inside the body to flow up and down without accumulating super-absorbent resin particles, while allowing the cooling air, water, and additives to flow up and down. Since stirring and contact with the agent are performed, contact and friction between the spade-shaped blade and the super absorbent resin particles and between the super absorbent resin particles can be reduced, and as a result, the super absorbent resin particles It is possible to prevent the breakage and the accompanying deterioration of physical properties.

Further, in the spade type cooler, a portion of the spade type blade, such as a center portion or a cutting edge, has a concave shape like a spoon or a shovel. This is advantageous in pumping up super absorbent resin particles compared to a paddle with a flat cutting edge, and as a result, the contact between super absorbent resin particles and cooling air and water is enhanced. This is done uniformly throughout the water-absorbing resin particles.

In addition, in the spade type cooler, even if agglomeration of superabsorbent resin particles occurs during the cooling and water addition, the agglomerated particles can be easily separated by the stirring force generated in multiple directions within the body. As a result, the content of coarse particles in the super absorbent resin particles can be reduced, and deviations in the physical properties and water absorption performance of the super absorbent resin can be prevented and minimized.

1 to 3 are schematic diagrams schematically showing the structure of a spade-shaped cooler used in the method for producing a superabsorbent resin according to the present invention in a side cross section, a front surface, and a rear surface, respectively. 1 to 3 are merely examples for explaining the present invention, and the present invention is not limited thereto.

Hereinafter, referring to FIGS. 1 to 3, the spade-type cooler 10 specifically has a transfer space into which the super absorbent resin particles having the surface crosslinked layer are transferred. a rotatable body part 1; and two nozzles provided in the body part 1 for injecting cooling air and water into the transfer space, respectively, namely a cooling air injection nozzle 2a and a water injection nozzle. 2b, one or more spade-shaped blades that are provided on the inner wall of the body part so as to be movable up and down, and that pump up the super absorbent resin particles on which the surface cross-linked layer is formed in the transfer space from bottom to top. type blade) 3 and a drive motor 4 connected to the body part 1 to provide a driving force, and the surface crosslinked layer is formed by vertically driving the spade-shaped blade 3 in the body part 1. After pumping up the super absorbent resin particles, the pumped super absorbent resin particles are caused to fall in the direction of gravity by the rotation of the body section 1, and cooling air and water are introduced into the transfer space of the body section 1. By contacting the superabsorbent resin particles with the surface cross-linked layer, cooling and hydration are simultaneously performed.

Specifically, the body portion 1 of the spade-type cooler includes a transfer space in which superabsorbent resin particles having a surface crosslinked layer are transferred and flowed.

Although the shape of the body portion 1 is not particularly limited, it may be cylindrical or drum-shaped, for example.

Further, the body part 1 is rotatable, so that the components present in the internal space of the body part can be stirred and mixed by the rotation of the body part.

The rotation of the body part 1 may be performed by the entire body part or by rotation of a certain part of the body part. For example, the entire body can be rotated by the driving force transmitted from the driving motor 4. As another example, rotating shafts are provided at the outer upper and lower parts of the body part 1 in the longitudinal direction of the body part, and when driving force is transmitted from a drive motor to the rotating shaft, the rotating shaft is rotated by the driving force. As a result, the body part can be rotated in a direction perpendicular to the longitudinal direction of the body part.

Further, when only a certain portion of the body part rotates, the body part includes a rotating part that is connected to a drive motor and rotates by a driving force transmitted from the drive motor, and a fixed part that does not rotate. As an example, the rotating part is located on the upper side of a body part into which the surface-crosslinked super absorbent resin particles and the cooling medium are input, and the fixed part is located in the body part from which the cooled super absorbent resin particles are discharged. It can be located below. Alternatively, the fixed part is located on the upper side of the body part into which the surface-crosslinked superabsorbent resin particles and the cooling medium are introduced, and the rotating part is located in the lower part from which the cooled superabsorbent resin particles are discharged. can do. Alternatively, as shown in FIG. 1, the rotating part 1a may be located in the middle of the body part, and the fixed part 1b may be located above and below the rotating part 1a, respectively.

The body portion 1 also has a super absorbent resin inlet for introducing super absorbent resin particles having a surface cross-linked layer formed thereon, and a super absorbent resin inlet for discharging cooled and hydrated super absorbent resin particles. and a water-absorbing resin discharge port. The position thereof is not particularly limited, and the super absorbent resin inlet is provided at one end of the body part, and the super absorbent resin inlet is provided at the other end of the body part. As an example, as shown in FIG. 1, a super absorbent resin inlet 1c is provided in the upper area of the body part 1 so that the super absorbent resin inside the body part 1 flows in one direction. A superabsorbent resin discharge port 1d is formed in the lower region of the body portion 1.

In addition, as shown in FIG. 1, the spade-shaped cooler has a discharge port that is inclined toward the discharge port 1d on the inner wall of the body portion so that the cooled and hydrated superabsorbent resin particles can be easily discharged. A discharge plate is further formed that is configured to be coupled to the discharge plate. In this case, when the cooled and hydrated superabsorbent resin particles accumulate on the discharge plate, they can be easily discharged to the discharge port due to the inclination of the discharge plate.

As still another example, the body part 1 includes an upper area where a super absorbent resin inlet 1c for introducing the super absorbent resin is located, and an upper area where the super absorbent resin particles are mixed with cooling air and water. It consists of a jacket area where cooling is performed by contact, and a lower area provided with a superabsorbent resin discharge port 1d for discharging cooled superabsorbent resin particles. In this case, the jacket area corresponds to the rotating part 1a, and the upper and lower areas each correspond to the fixed part 1b.

Further, the body portion 1 is provided with respective nozzles for injecting the cooling air and water, that is, a cooling air injection nozzle 2a and a water injection nozzle 2b. Thereby, the cooling air and water introduced through the nozzle are sprayed into the space of the body part. The nozzle may be selectively equipped with a nozzle opening/closing means or control means such as a valve or a switch that can control the input speed or spraying rate of cooling air and water, and the input amount or spray amount.

The formation position of the nozzle is not particularly limited, and as an example, in consideration of ease and uniformity of mixing with the super absorbent resin, there is a super absorbent resin inlet side, that is, an inlet. It is formed in the upper region of the body part, more specifically, in the fixing part 1b located on the upper side of the body part.

Further, on the inner wall of the body portion 1, there is a spade-shaped blade 3 provided so as to be movable up and down.

The spade-shaped blade 3 has a spoon or shovel shape, and is driven up and down while rotating together with the rotation of the body. This acts to pump up the superabsorbent resin particles existing in the transfer space of the body part from the bottom to the top, and the superabsorbent resin particles drawn up by the spade-shaped blade fall due to the rotation of the body part and gravity. While doing so, it contacts and mixes with the cooling air and water introduced into the space of the body.

One or more, two or more, three or more, or four or more spade-shaped blades 3 may be provided on the inner wall of the body, but the invention is not limited thereto. It can be determined appropriately by taking into consideration the size of the body part, etc.

Further, since the spade-shaped blade is driven up and down while rotating due to the rotation of the body, the driving speed of the spade-shaped blade is determined according to the rotational speed of the body. However, another drive speed control member may optionally be further included to control the drive speed of the spade-shaped blade.

Furthermore, the spade-type cooler 10 includes a drive motor 4 connected to the body part 1 and providing driving force, specifically, rotational driving force.

The spade-shaped cooler 10 also includes a super absorbent resin supply section (not shown) that stores and supplies super absorbent resin particles on which a surface cross-linked layer is formed; A cooling air supply section (not shown) supplied by a cooling air injection nozzle provided on the body; a water supply section (not shown) that stores water and supplies water through a water injection nozzle provided on the body of the cooler; (not shown); an additive nozzle (not shown) provided in the body of the cooler for additives to be added selectively during the cooling and water addition process; or an additive inlet 1e may optionally further include one or more of the following.

FIG. 4 is a schematic diagram schematically showing the mixing process that occurs within the body of the spade-type cooler during the cooling and water addition stages in the method for producing a superabsorbent resin according to the present invention. In FIG. 4, arrows indicate rotation of the body portion.

Referring to FIG. 4, when the surface-crosslinked superabsorbent resin particles 20 are introduced into the spade-shaped cooler having the above structure through the superabsorbent resin inlet, the spade-shaped blades in the body of the cooler are introduced. The super absorbent resin particles are pumped up from the bottom to the top by the vertical drive of step 3. Thereafter, the pumped up superabsorbent resin particles fall in the direction of gravity due to the rotation of the body, and are mixed with cooling air and water that are injected into the space of the body by a method such as spraying through a nozzle connected to the body. Contact. At this time, the superabsorbent resin particles are cooled by heat exchange with the cooling air and water, and at the same time, the superabsorbent resin particles are hydrated by the water. In particular, in the spade-type cooler according to the present invention, the super absorbent resin particles in the body part fall uniformly due to gravity, so the contact and water addition are uniformly carried out over the entire super absorbent resin particles. Deviations in the physical properties and water absorption performance of the resin can be prevented and minimized.

On the other hand, the temperature of the cooling air introduced into the spade type cooler is 10°C to 60°C, and the temperature is 0.01 m ³ /h based on the input amount of 1 kg of the super absorbent resin on which the surface crosslinked layer is formed. The cooling air is injected through a cooling air injection nozzle provided in the body at a speed of /kg to 0.25m ³ /h/kg. When cooling air is introduced under the above conditions, an excellent cooling effect can be exhibited. More specifically, the temperature of the cooling air is 10°C or higher, or 15°C or higher, or 20°C or higher, or 25°C or higher, or 30°C or higher and 60°C or lower, or 50°C or lower, or 40°C or lower, or 35°C or lower, and 0.01 m ³ /h/kg or more, or 0.05 m 3 /h/kg or more, or 0.1 ^{m 3 /} h/kg or more based on 1 kg of superabsorbent resin input, and , 0.25 m ³ /h/kg or less, 0.2 m ³ /h/kg or less, or 0.15 m ³ /h/kg or less through a cooling air injection nozzle provided in the body.

Further, the temperature of the water is 10° C. to 60° C., and the water is added in an amount of 2 to 20 parts by weight based on 100 parts by weight of the super absorbent resin particles on which the surface crosslinked layer is formed. When water is added under the above conditions, it is possible to exhibit a hydration effect as well as a cooling effect on the superabsorbent resin particles on which the surface crosslinked layer is formed. More specifically, the temperature of the water is 10°C or higher, or 15°C or higher, or 20°C or higher, or 23°C or higher and 60°C or lower, or 50°C or lower, or 40°C or lower, or 30°C or lower, Alternatively, the temperature is 27°C or lower, and even more specifically, room temperature (25±2°C). Furthermore, the amount of water is 2 parts by weight or more, or 5 parts by weight or more and 20 parts by weight or less, or 10 parts by weight or less, based on 100 parts by weight of the super absorbent resin particles on which the surface crosslinked layer is formed. Injected.

Further, in the spade type cooler, the body portion 1 or the rotating portion 1a within the body portion can rotate at a speed of 5 to 50 times per minute (or 5 to 50 rpm). On the other hand, the rotation speed of the body portion or the rotating portion within the body portion once per minute corresponds to 1 rpm.

When rotating under the above conditions, the superabsorbent resin particles can fall at a speed sufficient to contact cooling air and water. More specifically, the body part or the rotating part within the body part rotates at least 5 times per minute, or at least 10 times, or at least 20 times and at most 50 times, or at most 40 times, or at most 30 times per minute. Can rotate at high speed. On the other hand, in the present invention, the spade-type cooler may include a rotational speed control device (such as an inverter) that is located between the body portion and the drive motor and controls the rotational speed of the body portion or a rotating portion within the body portion. (not shown) may optionally be further provided.

Furthermore, in the manufacturing method according to the present invention, one or more additives may be further added for improving the cooling efficiency during the cooling step, improving the water content and physical properties of the superabsorbent resin, and the like.

Specifically, the additive may be an inorganic substance. Specific examples include silica, clay, alumina, silica-alumina composites, titania, zinc oxide, and aluminum sulfate, and any one or a mixture of two or more of these can be used. The inorganic material can act as an anti-caking agent that increases the water content of the superabsorbent resin particles and improves the anti-caking efficiency.

When the inorganic substance is further added, an additive nozzle (not shown) or an additive nozzle (not shown) is installed in the body of the spade-type cooler to introduce the additive into the transfer space of the body. The agent may be injected through the superabsorbent resin inlet 1e, or the agent may be mixed with the superabsorbent resin on which the surface crosslinked layer is formed and injected in the form of a mixture through the superabsorbent resin inlet.

Conventionally, when manufacturing superabsorbent resins, inorganic substances were mixed using a blade mixer to improve the water content. In this case, the dry mixing of the inorganic substances made homogeneous mixing difficult, and as a result, deviations in the physical properties of the superabsorbent resin produced occurred.

In contrast, in the present invention, wet mixing is performed by cooling using a spade-type cooler and adding water during the water addition process, and as a result, homogeneous mixing with the super absorbent resin is possible, and the product can be manufactured. The physical properties of the super absorbent resin can be uniformly improved.

The inorganic substance is added in an amount of 0.02 to 1.0 parts by weight based on 100 parts by weight of the super absorbent resin particles on which the surface crosslinked layer is formed. If the amount of inorganic material added is too small, it will be difficult to obtain a sufficient hydration effect by adding inorganic material, whereas if the amount of inorganic material added is too high, the water content of the superabsorbent resin will be excessively increased. This may actually reduce the water absorption performance. More specifically, the inorganic substance is 0.02 parts by weight or more, or 0.05 parts by weight or more, or 0.1 parts by weight, based on 100 parts by weight of the super absorbent resin particles on which the surface crosslinked layer is formed. It is added in an amount of not less than 1.0 part by weight, or not more than 0.7 part by weight, or not more than 0.5 part by weight.

In addition to the above substances, additives such as a liquid permeability improver and a fluidity improver may be selectively added, but the present invention is not limited thereto.

The method of introducing the additive is not particularly limited, and the additive may be introduced through an additive nozzle that is provided in the body part and allows the additive to be introduced into the space of the body part, or it may be mixed together with the super absorbent resin. It may also be put in.

By performing the cooling and hydration steps, the water content of the super absorbent resin finally produced is improved, the content of coarse particles is reduced, and as a result, higher quality super absorbent resin products are produced. can do.

Specifically, after the cooling and hydration step, the content of coarse particles having a particle size of more than 850 μm in the cooled and hydrated superabsorbent resin particles is 3% by weight or less, or 1% by weight or less, or 0.7% by weight or less, or 0.5% by weight or less, or 0.3% by weight. Since the lower the content of coarse particles, the better, the lower limit thereof is not particularly limited, but may be, for example, 0.01% by weight or more, or 0.1% by weight or more.

On the other hand, the content (wt%) of coarse particles having a particle size of more than 850 μm can be determined by classifying cooled and hydrated superabsorbent resin particles using a method such as using a standard molecular sieve according to ASTM regulations. After separating the coarse particles having the same diameter, their weight was measured, and the weight ratio of the coarse particles to the total weight of the cooled and hydrated superabsorbent resin particles was determined and expressed as a percentage. The specific measurement method is as explained in the following experimental example.

Additional Step The manufacturing method according to the present invention may further include, after the cooling and hydration step, classifying the cooled and hydrated superabsorbent resin.

The classification step may be performed by a normal method such as using a standard molecular sieve according to ASTM regulations, or by such a classification step, coarse particles with a particle size of more than 850 μm are separated and removed, and coarse particles with a particle size of 150 to 850 μm are separated and removed. It is possible to obtain normal particles of super absorbent resin having the following properties.

In addition, the manufacturing method according to the present invention further includes, after the classification step, the step of pulverizing the separated coarse particles and mixing the crushed coarse particles with the normal particles of the superabsorbent resin separated in the classification step. can be included.

The coarse particles are pulverized using a conventional pulverization method, except that the pulverized coarse particles have a particle size comparable to that of normal particles.

Specifically, there are a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, and a disc mill. It is carried out using a crusher such as a disc mill, a shred crusher, a crusher, a chopper, or a disc cutter, but if the crusher is It is not limited to the example described above.

Alternatively, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, or the like may be used as the crusher. However, it is not limited to the above example.

Thereafter, the pulverized coarse particles and the normal particles of the superabsorbent resin may be mixed using a normal mixing method, and the mixing ratio may be adjusted appropriately within a range that does not reduce the water absorption performance of the superabsorbent resin. Determinable.

According to the present invention, a superabsorbent resin produced by the above production method is provided.

The superabsorbent resin produced by the above production method has a high water content and a low content of coarse particles having a particle size of more than 850 μm even without a separate classification step. As a result, when manufacturing products using the superabsorbent resin, the amount of fine powder generated is small.

Furthermore, the superabsorbent resin has water retention capacity (CRC) and water absorption capacity under pressure (AUP), which are various water absorption properties, at the same level or higher than superabsorbent resins produced by conventional methods.

Furthermore, the superabsorbent resin exhibits a uniform particle size with a narrow particle size distribution, has a low content of water-soluble components (EC), and has good liquid permeability, rewet characteristics, and water absorption rate. All are excellent.

Specifically, the superabsorbent resin includes a polymer in which a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent are crosslinked, and at least a portion of the acidic group of the polymer is It is neutralized and includes a surface crosslinked layer formed on the polymer by additionally crosslinking the polymer with a surface crosslinking agent, and satisfies the following conditions (i) to (iii). May be:

(i) Water content is 1.2% to 5% by weight based on the total weight of the super absorbent resin
(ii) Centrifugal water retention capacity (CRC) measured by EDANA WSP241.3: 30-45 g/g
(iii) Average water absorption capacity under pressure of 0.3 psi measured by EDANA method WSP242.3: 29 to 40 g/g, standard deviation of water absorption capacity under pressure of 0.3 psi: 1 or less.

More specifically, the superabsorbent resin has a water content of 1.2% by weight or more, 1.4% by weight or more, or 1.5% by weight or more, based on the total weight of the superabsorbent resin. or 1.7 wt% or more, or 1.8 wt% or more, or 1.9 wt% or more and 5 wt% or less, or 3 wt% or less, or 2.6 wt% or less, or 2.5 wt% or less than 2% by weight. By having a higher water content than conventional products, damage to the surface due to friction between superabsorbent resin particles during the manufacturing process is reduced, and this can prevent the physical properties of the superabsorbent resin from deteriorating. . In addition, the amount of fine powder generated during the product manufacturing process using the superabsorbent resin is reduced, process stability and productivity are improved, and product quality can be improved.

The moisture content is the amount of water relative to the total weight of the superabsorbent resin, and is the weight loss due to evaporation of water in the superabsorbent resin during the drying process by raising the temperature of the superabsorbent resin using infrared heating. can be measured and calculated using the following formula 1. The specific measurement method and measurement conditions will be explained in detail in the following experimental examples.

[Formula 1]
Moisture content (wt%) = [(Ao-At)/Ao] x 100

In the above formula, At is a method in which the temperature is raised from room temperature to 180°C and then maintained at 180°C, and the total drying time is set to 40 minutes, including 5 minutes during the temperature rise stage, and the drying process is performed. Ao is the weight of the super absorbent resin after drying, which was measured after drying, and Ao is the weight of the super absorbent resin before drying.

Further, more specifically, the superabsorbent resin has a centrifugal water retention capacity (CRC) of 30 g for 30 minutes in physiological saline (0.9% by weight aqueous sodium chloride solution) as measured by EDANA method WSP241.3. /g or more, or 35g/g or more, or 36.5g/g or more, or 37g/g or more. The higher the CRC value is, the better it is, and there is no practical upper limit, but as an example, it is 45 g/g or less, or 40 g/g or less. The specific method and conditions for measuring the CRC will be explained in detail in the following experimental examples.

Furthermore, the superabsorbent resin was measured by EDANA method WSP242.3 for 1 hour under 0.3 psi of the superabsorbent resin in physiological saline (0.9% by weight aqueous sodium chloride solution). The average pressurized water absorption capacity (0.3AUP) of 29g/g or more, or 29.3g/g or more, or 29.5g/g or more, or 30g/g or more and 40g/g or less, or 35g/g or less than or equal to 32 g/g. In addition, the standard deviation of the pressurized water absorption capacity of 0.3 psi is 1 or less, or 0.7 or less, or 0.5 or less, and the smaller the standard deviation value, the better, and there is no practical lower limit limit. is, for example, 0.1 or more, or 0.2 or more. The specific method and conditions for measuring the 0.3C AUP will be explained in detail in the following experimental examples.

In addition, when an inorganic material such as silica is further added during the cooling and hydration stages during the production of the superabsorbent resin, high caking prevention efficiency can be exhibited.

Specifically, the superabsorbent resin has an average caking prevention efficiency (A/C) of 85% or more and a standard deviation of 10 or less, which is calculated using the following formula 2. More specifically, the average anti-caking efficiency (A/C) is 85% or more, or 90% or more, or 95% or more. The higher the caking prevention efficiency value is, the better it is, and there is no practical upper limit, but as an example, it is 100% or less, or 98% or less. Further, the standard deviation of the caking prevention efficiency is more specifically 10 or less, or 9.5 or less, or 9 or less, and the smaller the standard deviation value is, the better it is, and there is no practical lower limit. is, for example, 1 or more, or 5 or more.

In the above formula,
W ₅ is the weight (g) of a Petri dish with a diameter of 90 mm and a height of 15 mm,
In _S1 , 2±0.01 g of superabsorbent resin sample was evenly applied to a Petri dish whose weight was measured at _W5 , and then the Petri dish coated with the sample was heated to a temperature of 40°C and a humidity of 80% RH. After leaving it in the constant temperature and humidity chamber for 10 minutes, take it out and turn it over on A4 paper. After 5 minutes, the weight (g) of the superabsorbent resin sample that fell on the A4 paper was measured. can be,
S ₂ is the weight (g) of the Petri dish at the time when S ₁ was measured.

Accordingly, the superabsorbent resin can be appropriately used in sanitary materials such as diapers, especially ultra-thin sanitary materials with reduced pulp content.

Below, preferred embodiments are presented for understanding the invention. However, the following examples are only for illustrating the present invention, and the content of the present invention is not limited by the following examples.

Manufacturing example 1
Production of hydrogel polymer In a 2 L glass container equipped with a stirrer and a thermometer, 100 g of acrylic acid, 0.35 g of pentaerythritol allyl ether as an internal crosslinking agent, and 226 g of water were mixed with stirring. At this time, the reaction temperature was maintained at 5°C. The resulting mixture was supplied with nitrogen at 1000 cc/min for 1 hour. Thereafter, as polymerization initiators, 1.3 g of 0.3% hydrogen peroxide aqueous solution, 1.5 g of 1% ascorbic acid aqueous solution, and 3.0 g of 2% 2,2'-azobisamidinopropane dihydrochloride aqueous solution were added. At the same time, 1.5 g of a 0.01% iron sulfate aqueous solution was added as a reducing agent and mixed. A polymerization reaction was started with the resulting mixture, and after the temperature of the polymer reached 85°C, a hydrogel polymer was produced by polymerizing in an oven at 90±2°C for about 6 hours (water content: hydrogel 70% by weight based on the total weight of the polymer).

Production of water-containing super absorbent resin particles 1000 g of the obtained water-containing gel polymer was subjected to a micronization device (Micronizer) (F200, Karl Schnell) equipped with a perforated plate containing a large number of holes with a hole size of 6 mm. While rotating at 1500 rpm, the mixture was passed through four times to be atomized. At this time, no additives were added during the first pass, 400 g of 32% NaOH aqueous solution was added during the second pass, and 37.5 g of 15% Na ₂ SO ₄ aqueous solution was added during the third pass. During the round-pass, Glycerol Monolaurate (GML) as a surfactant was dissolved in water at 60°C in the form of an aqueous solution (1.5 w%), and GML was added in proportion to 100 parts by weight of the hydrogel polymer. It was added in an amount of 0.4 parts by weight. As a result, hydrated superabsorbent resin particles were obtained (water content: 68% by weight of the total weight of the hydrated superabsorbent resin particles).

Production of dry superabsorbent resin particles The hydrated superabsorbent resin particles obtained as a result of the atomization were put into a rotary kiln fluidized dryer (Rotary kiln, manufactured by WOONGBI MACHINERY CO., LTD.) and then heated at 150°C. , for 60 minutes with stirring at a speed of 100 rpm to obtain dry super absorbent resin particles (water content: based on the total weight of dry super absorbent resin particles: 11% by weight).

Formation of surface crosslinked layer Next, for 100 g of the dry superabsorbent resin particles, 4 g of water, 6 g of methanol, 0.30 g of ethylene glycol diglycidyl ether (Glyether (registered trademark) EJ-1030, manufactured by JSI), and propylene. A surface cross-linking solution prepared by adding 0.1 g of glycol and 0.2 g of aluminum sulfate was mixed for 1 minute, and the surface cross-linking reaction was allowed to proceed at 140°C for 50 minutes to form a surface-crosslinked super absorbent resin. Obtained.

Manufacturing example 2
When forming the hydrogel polymer of Production Example 1, 100 g of acrylic acid, 140 g of 31.5% by weight sodium hydroxide (NaOH), 0.20 g of polyethylene glycol diacrylate, 0.12 g of sodium persulfate as a thermal polymerization initiator, A monomer composition was prepared by mixing 0.01 g of diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide as a photopolymerization initiator and 40 g of water, and this was placed in a square reaction box measuring 30 cm in width and 30 cm in length. Surface crosslinking was carried out in the same manner as in Production Example 1, except that the polymer was placed in a container and irradiated with ultraviolet rays having an intensity of 10 mW/cm ² to cause a polymerization reaction for 60 seconds to produce a hydrogel polymer. A super absorbent resin was obtained.

Manufacturing example 3
The production of the hydrogel polymer according to Production Example 1 was carried out in the same manner as in Production Example 1, except that GMS (glycerol monostearate) was used instead of GML as a surfactant. A surface-crosslinked superabsorbent resin was obtained.

Example 1
The surface-crosslinked superabsorbent resin produced in Production Example 1 was subjected to a cooling process under the conditions listed in Table 1 below.

Specifically, after the surface-crosslinked superabsorbent resin produced in the above production example was put into a spade-type cooler having the structure shown in FIG. A cooling process was performed by injecting cooling air through a nozzle. At this time, the temperature of the cooling air introduced into the cooler is 35° C., and the injection rate is 0.1 m ³ /h/kg based on 1 kg of the surface-crosslinked super absorbent resin. In addition, during the cooling process, water was introduced through a nozzle separately provided inside the cooler, and the water addition process was performed simultaneously. At this time, the water temperature was room temperature (25±2℃), the amount added was 5 parts by weight based on 100 parts by weight of the surface-crosslinked super absorbent resin, and the rotation speed of the body was 1 minute. 20 times per rotation (20 rpm).

As a result, the cooled and hydrated superabsorbent resin particles were collected and classified to separate them into normal superabsorbent resin particles with a particle size of 150 to 850 μm and coarse particles with a particle size of more than 850 μm. The separated coarse particles were pulverized once using a roll mill, and then mixed with the normal particles of the super absorbent resin to produce a super absorbent resin.

Example 2
As described in Table 1 below, during the cooling process, fumed silica was added as an additive through a separate inlet so as to be mixed with the surface-crosslinked superabsorbent resin introduced into the cooler. A cooling process was carried out using a spade type cooler in the same manner as in Example 1, except for adding Aerosil 200 (Aerosil 200, manufactured by EVONIK). At this time, the temperature of the cooling air introduced into the cooler is 35°C, and the injection rate is 0.1 m ³ /h/kg based on 1 kg of surface-crosslinked super absorbent resin. The rotation speed was 20 times per minute (20 rpm). Further, during the cooling process, water and fumed silica (Aerosil 200, manufactured by EVONIK) were respectively introduced through nozzles separately provided inside the cooler. At this time, the temperature of the water to be added is room temperature (25±2° C.), and the amount to be added is 5 parts by weight based on 100 parts by weight of the surface-crosslinked superabsorbent resin. Further, the fumed silica was added in an amount of 0.1 part by weight based on 100 parts by weight of the super absorbent resin.

As a result, the cooled and hydrated superabsorbent resin particles were collected and classified to separate them into normal superabsorbent resin particles with a particle size of 150 to 850 μm and coarse particles with a particle size of more than 850 μm. The separated coarse particles were pulverized once using a roll mill, and then mixed with normal particles of the superabsorbent resin to produce a superabsorbent resin.

Examples 3 to 7
A superabsorbent resin was produced in the same manner as in Example 1, except that it was carried out under the conditions shown in Table 1 below.

Comparative example 1
As shown in Table 1 below, the surface-crosslinked super absorbent resin particles produced in Production Example 1 were placed in a paddle-type cooler (NPD-14W ^TM , manufactured by Nara), and 5 parts by weight of water at room temperature (25±2°C) was poured into the double jacket inside the paddle type cooler without a nozzle per 100 parts by weight of the surface-crosslinked super absorbent resin, and the water was heated 10 times per minute. Mixing was performed by driving the paddle at speed (10 rpm) and a cooling step was performed (no silica input). A super absorbent resin was produced in the same manner as in Example 1, except that after the cooling step, the steps of classification, coarse particle pulverization, and mixing of the super absorbent resin with normal particles were not performed.

Comparative example 2
As described in Table 1 below, the surface-crosslinked super absorbent resin particles produced in Production Example 1 were placed in a paddle-type cooler (NPD-14W ^TM , manufactured by Nara), and 5 parts by weight of water at room temperature (25 ± 2°C) per 100 parts by weight of the surface-crosslinked super absorbent resin was poured into the double jacket through a nozzle provided inside the double jacket, and the mixture was heated at a rate of 10 times per minute ( A super absorbent resin was produced in the same manner as in Example 1, except that the paddles were driven at a speed of 10 rpm for mixing and the cooling process was performed.

Comparative example 3
As described in Table 1 below, the super absorbent resin particles produced in Production Example 1 were put into a paddle-type cooler, and the particles were placed inside the paddle-type cooler (NPD-14W ^TM , manufactured by Nara Corporation). 5 parts by weight of water at room temperature (25±2°C) was poured into the double jacket for 100 parts by weight of the surface-crosslinked super absorbent resin through the nozzle, and the water was paddled at a rate of 10 times per minute (10 rpm). was driven to mix, and a cooling process was performed.

After completion, the cooled superabsorbent resin particles were put into a Ploughshare-type mixer (CoriMix® CM, manufactured by Leodige) and mixed with fumed silica (Aerosil200, manufactured by EVONIK). 0.1 part by weight of 100 parts by weight of super absorbent resin was added and mixed by driving a Plowshare at a speed of 200 times per minute (200 rpm).

The resulting mixture was classified to separate normal particles of the superabsorbent resin having a particle size of 150 to 850 μm and coarse particles having a particle size of more than 850 μm. The separated coarse particles were pulverized once using a roll mill, and then mixed with normal particles of the superabsorbent resin to produce a superabsorbent resin.

In the above table, "parts by weight" is a relative content ratio based on 100 parts by weight of the surface-crosslinked superabsorbent resin.

Experimental example 1
The water absorption performance of the super absorbent resins finally produced in the Examples and Comparative Examples was evaluated by the following method.

Unless otherwise specified, all physical property evaluations below were performed at constant temperature and humidity (23 ± 1°C, relative humidity 50 ± 10%), and physiological saline or salt water contained 0.9% by weight sodium chloride (NaCl). means an aqueous solution.

Furthermore, unless otherwise specified, physical property evaluations of the superabsorbent resins finally produced were performed on resins having a particle size of 150 μm to 850 μm that were classified using an ASTM standard sieve.

(1) Water Content The water content of the super absorbent resins finally produced in the Examples and Comparative Examples was measured. The water content is the water content relative to the total weight of the superabsorbent resin, and was calculated using Equation 1 below.

Specifically, the weight loss due to water evaporation in the superabsorbent resin was measured and calculated during the process of raising the temperature of the superabsorbent resin by infrared heating and drying it. At this time, the drying conditions were such that the temperature was raised from room temperature to 180° C. and then maintained at 180° C., and the total drying time was set to 40 minutes, including 5 minutes during the temperature rising stage. The weight of the superabsorbent resin before and after drying was measured and calculated using Equation 1 below.

[Formula 1]
Moisture content (wt%) = [(Ao-At)/Ao] x 100

In the above formula, At is the weight of the super absorbent resin after drying, and Ao is the weight of the super absorbent resin before drying.

(2) Centrifuge Retention Capacity (CRC)
The water retention capacity of the superabsorbent resins finally produced in the Examples and Comparative Examples was measured in accordance with the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP241.3.

Specifically, the superabsorbent resin W ₀ (g) (approximately 0.2 g) obtained in Examples and Comparative Examples was uniformly placed in a nonwoven envelope, sealed, and then exposed to physiological conditions at room temperature. Soaked in saline (0.9% by weight). After 30 minutes, the envelope was drained for 3 minutes using a centrifuge at 250 G, and the mass W ₂ (g) of the envelope was measured. Moreover, after performing the same operation without using the resin, the mass W ₁ (g) at that time was measured.

CRC (g/g) was calculated using the following formula 3 using each obtained mass.

[Number 3]
CRC (g/g) = {[W ₂ (g)-W ₁ (g)]/W ₀ (g)}-1

(3) Absorption under Pressure (AUP)
The water absorption capacity under pressure of 0.3 psi of the super absorbent resins finally produced in the Examples and Comparative Examples was measured by EDANA method WSP242.3.

Specifically, a 400-mesh wire mesh made of stainless steel was attached to the bottom of a plastic cylinder with an inner diameter of 25 mm. The piston is capable of uniformly dispersing superabsorbent resin W ₀ (g) (0.9 g) onto a wire mesh under conditions of room temperature and 50% humidity, and evenly applying a load of 0.3 psi on top of it. The diameter is slightly smaller than 25 mm, and there is no gap with the inner wall of the cylinder, so vertical movement is not hindered. At this time, the weight W ₃ (g) of the device was measured.

A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a Petri dish with a diameter of 150 mm, and physiological saline containing 0.9% by weight sodium chloride was placed at the same level as the top surface of the glass filter. A piece of filter paper with a diameter of 90 mm was placed on top of it. The measuring device was placed on the filter paper, and the liquid was allowed to absorb under load for 1 hour. After one hour, the measuring device was lifted and its weight W ₄ (g) was measured.

Using each obtained mass, the pressurized water absorption capacity (g/g) was calculated using the following formula 4.

[Formula 4]
AUP (g/g) = [W ₄ (g) - W ₃ (g)] / W ₀ (g)

The above measurement was repeated five times, and the average value and standard deviation were determined.

(4) Content of coarse particles having a particle size of more than 850 μm (#20 upper) The super water absorbent resin particles obtained after the cooling and hydration steps in the Examples and Comparative Examples were A standard sieve with size graduations of 600 μm (30 mesh), 300 μm (50 mesh), and 150 μm (100 mesh) was used to classify coarse particles with a particle size of more than 850 μm. After measuring the weight, the weight ratio of the coarse particles to the total weight of the cooled and hydrated superabsorbent resin particles was expressed as a percentage (weight %).

As a result of the experiment, Example 1 had a higher water content than Comparative Example 1, but there was no decrease in water absorption performance such as CRC and AUP. Furthermore, compared to Comparative Example 2, the content of coarse particles having a particle size of more than 850 μm was reduced, and more excellent effects were exhibited in terms of CRC and AUP water absorption performance.

Further, in comparison with Comparative Example 3, Example 2 had a reduced content of coarse particles having a particle size of more than 850 μm, and exhibited excellent effects in terms of CRC and AUP water absorption performance. Furthermore, compared to Comparative Example 3, the physical property deviation of AUP was also smaller.

Experimental example 2
In order to evaluate the caking prevention effect of adding inorganic substances during the production of super absorbent resins, the following method was used to prevent caking on the final super absorbent resins of Examples and Comparative Examples manufactured using inorganic substances. (A/C, Anti-caking) efficiency was measured.

<Measuring device>
-Electronic scale (accuracy: 0.01g)
- Constant temperature and humidity chamber (temperature: 40℃, humidity: 80%RH)
-Petri dish (Petri dish, Ф: 90mm, height: 15mm)
- Stopwatch - A4 paper

<Measurement method>
(1) First, the weight (W ₅ ) of the prepared Petri dish was measured.
(2) Next, 2±0.01 g of the superabsorbent resin produced in the above Example or Comparative Example was evenly applied as a sample to the weighed Petri dish.
(3) Thereafter, the Petri dish containing the superabsorbent resin sample was placed in a constant temperature and humidity chamber set at a temperature of 40° C. and a humidity of 80% RH and left for 10 minutes.
(4) After 10 minutes, the Petri dish was taken out of the constant temperature and humidity chamber, turned upside down onto a prepared A4 sheet of paper, and left for 5 minutes.
(5) After 5 minutes have passed, measure the weight of the superabsorbent resin sample (S ₁ ) dropped onto A4 paper and the weight of the Petri dish (S ₂ ) at this time, and calculate the caking prevention efficiency using the following formula 2. was calculated and rounded to one decimal place.

In the above formula,
W ₅ is the weight (g) of a Petri dish with a diameter of 90 mm and a height of 15 mm,
In _S1 , 2±0.01 g of superabsorbent resin sample was evenly applied to a Petri dish whose weight was measured at _W5 , and then the Petri dish coated with the sample was heated to a temperature of 40°C and a humidity of 80% RH. After leaving it in the constant temperature and humidity chamber for 10 minutes, take it out and turn it over on A4 paper. After 5 minutes, the weight (g) of the superabsorbent resin sample that fell on the A4 paper was measured. can be,
S ₂ is the weight (g) of the Petri dish at the time when S ₁ was measured.

The above measurement was repeated five times, and the average value and standard deviation were determined.

As a result of the experiment, Examples 2 to 7 exhibited markedly increased caking prevention efficiency compared to Comparative Example 3, and the deviations in physical properties were also small.

1: Body part 1a: Rotating part 1b: Fixed part 1c: Super absorbent resin inlet 1d: Super absorbent resin outlet 1e: Additive inlet 2a: Cooling air injection nozzle 2b: Water injection nozzle 3: Spade Type blade 4: Drive motor 10: Spade type cooler 20: Super absorbent resin particles

Claims (18)

forming a hydrogel polymer in which a water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent are crosslinked and polymerized;
A step of producing hydrated superabsorbent resin particles by atomizing the hydrated gel polymer;
drying the hydrated superabsorbent resin particles to produce dry superabsorbent resin particles;
adding a surface crosslinking agent to the dry superabsorbent resin particles and reacting them to form a surface crosslinked layer on at least a portion of the surface of the superabsorbent resin particles;
cooling and adding water to the superabsorbent resin particles on which the surface crosslinked layer has been formed using a spade type cooler;
The spade-shaped cooler includes a transfer space into which the super absorbent resin particles having the surface cross-linked layer are transferred, and includes a rotatable body part and a rotatable body part provided in the body part to accommodate the transfer space. Two nozzles for injecting cooling air and water into the interior, respectively, are provided on the inner wall of the body portion so as to be movable up and down, and the superabsorbent resin particles on which the surface cross-linked layer is formed in the transfer space are moved from bottom to top. a super water absorbent material comprising one or more spade-shaped blades for recessing, and a drive motor connected to the body part to provide driving force, wherein the surface cross-linked layer is formed by the spade-shaped blades in the body part. After pumping up the resin particles, the pumped super absorbent resin particles are caused to fall in the direction of gravity by the rotation of the body section, and are brought into contact with the cooling air and water introduced into the transfer space of the body section. , cooling and adding water to the super absorbent resin particles on which the surface crosslinked layer has been formed;
Method for producing super absorbent resin. The temperature of the cooling air is 10° C. to 60° C., and the air flow rate is 0.01 m ³ /h/kg to 0.25 m ³ /h/, based on the input amount of 1 kg of super absorbent resin particles on which the surface crosslinked layer is formed. is fed into the cooler at a rate of kg,
A method for producing a superabsorbent resin according to claim 1. The temperature of the water is 10° C. to 60° C., and the water is added in an amount of 2 to 20 parts by weight based on 100 parts by weight of the super absorbent resin particles on which the surface crosslinked layer is formed.
A method for producing a superabsorbent resin according to claim 1. The body part rotates at a speed of 5 to 50 times per minute.
A method for producing a superabsorbent resin according to claim 1. During the cooling and water addition, an inorganic substance is further mixed,
The inorganic substance is introduced through an additive nozzle that is provided in the body part and allows the additive to be introduced into the space of the body part, or is mixed with a super absorbent resin and introduced.
A method for producing a superabsorbent resin according to claim 1. The inorganic substance is one or more selected from the group consisting of silica, clay, alumina, silica-alumina composite, titania, zinc oxide, and aluminum sulfate.
The method for producing a superabsorbent resin according to claim 5. Forming the hydrogel polymer includes:
neutralizing at least some of the acidic groups of the water-soluble ethylenically unsaturated monomer; a water-soluble ethylenically unsaturated monomer having the at least partially neutralized acidic groups; an internal crosslinking agent; and a step of polymerizing a monomer composition containing a polymerization initiator to form a hydrogel polymer, or a water-soluble ethylenically unsaturated monomer having an acidic group, internally crosslinked. polymerizing a monomer composition containing a polymerization agent and a polymerization initiator to form a polymer in which the water-soluble ethylenically unsaturated monomer having an acidic group and an internal crosslinking agent are crosslinked and polymerized; and neutralizing at least a portion of the acidic groups of the polymer to form a hydrogel polymer.
A method for producing a superabsorbent resin according to claim 1. The drying is performed by a moving type.
A method for producing a superabsorbent resin according to claim 1. The drying may be performed using a horizontal-type mixer dryer, a rotary kiln, a rotary dryer, a paddle dryer, or a steam tube dryer. ) is performed using
A method for producing a superabsorbent resin according to claim 1. The atomization is performed by an atomization device,
The atomization device includes:
a body portion including a transfer space into which the hydrogel polymer is transferred;
a screw member rotatably provided inside the transfer space to move the hydrogel polymer;
a drive motor that provides rotational driving force to the screw member;
a cutter member provided in the body portion to crush the hydrogel polymer;
a perforated plate in which a large number of holes are formed for discharging the hydrogel polymer crushed by the cutter member to the outside of the body part;
The method for producing a superabsorbent resin according to any one of claims 1 to 9. The atomization is performed two or more times,
A method for producing a superabsorbent resin according to claim 1. The atomization is carried out in the presence of a surfactant,
A method for producing a superabsorbent resin according to claim 1. The surfactant includes a compound represented by the following chemical formula 2 or a salt thereof,
The method for producing a super absorbent resin according to claim 12.
In the chemical formula 2,
A ₁ , A ₂ and A ₃ are each independently a single bond, carbonyl,
and one or more of these is carbonyl or
, where m1, m2 and m3 are each independently an integer from 1 to 8,
are connected to each adjacent oxygen atom,
is connected to adjacent R ₁ , R ₂ and R ₃ , respectively,
R ₁ , R ₂ and R ₃ are each independently hydrogen, a straight-chain or branched alkyl having 6 to 18 carbon atoms, or a straight-chain or branched alkenyl having 6 to 18 carbon atoms;
n is an integer from 1 to 9. During the atomization, one or more additives selected from the group consisting of metal hydroxides and metal salts are added.
A method for producing a superabsorbent resin according to claim 1. The metal hydroxide is sodium hydroxide or potassium hydroxide,
The metal salt is sodium sulfite, sodium persulfate, potassium persulfate or ammonium persulfate,
The method for producing a super absorbent resin according to claim 14. After the cooling and hydration step, the content of coarse particles with a particle size of more than 850 μm is 3% by weight or less based on the total weight of the superabsorbent resin particles obtained as a result.
A method for producing a superabsorbent resin according to claim 1. After the cooling and water addition steps, the resulting superabsorbent resin particles are classified and separated into coarse particles with a particle size of more than 850 μm and normal particles of superabsorbent resin with a particle size of 150 to 850 μm. The method further includes the step of pulverizing the coarse particles and mixing them with normal particles of the super absorbent resin.
A method for producing a superabsorbent resin according to claim 1. The superabsorbent resin satisfies the following conditions (i) to (iii):
A method for producing a superabsorbent resin according to claim 1:
(i) Water content: 1.2 to 5% by weight based on the total weight of the super absorbent resin
(ii) Centrifugal water retention capacity measured by EDANA WSP241.3: 30-45 g/g
(iii) Average water absorption capacity under pressure of 0.3 psi measured by EDANA method WSP242.3: 29 to 40 g/g, standard deviation of water absorption capacity under pressure of 0.3 psi: 1 or less.

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